When validating a FunctionCall we can trigger an assert if we are not
currently within a function body. This CL adds verification that we are
within a function before attempting to add a function call.
Issue 1789.
Many of the files have using std::<foo> statements in them, but then the
use of <foo> will be inconsistently std::<foo> or <foo> scattered
through the file. This CL removes all of the using statements and
updates the code to have the required std:: prefix.
This CL removes the two diag() overloads and leaves only the version
which accepts an Instruction. This is safer as we never use the
implicit location from the validation state.
This CL updates the diag() calls in validate_cfg to provide the
associated instruction. This fixes a couple places where we output the
last line of the file instead of the instruction as the disassembly.
This CL changes validate.cpp to use diag providing an explicit
instruction. This changes the result of the function end checks to not
output a disassembly anymore as printing the last line of the module
didn't seem to make sense.
Currently, some instructions will be missing from the list of
ordered_instructions. This will cause issues due to the debug change
which passed the last instruction into subsequent passes.
This CL moves the addition to the ordered list out of the
RegisterInstruction method into AddOrderedInstruction. This method is
called first in ProcessInstruction and the CapabilitiesPass and IdPass
are updated to take an Instruction parameter.
This CL removes the redundant operator name from the error messages in
validate_composites. The operator will be printed on the next line with
the disassembly.
This CL splits the switch in ImagePass into individual validate
functions. The error messages have been updated to drop the
suffix/prefix of the opcode name since it will be displayed in the
disassembly.
This CL updates the code to pull a valid instruction for the line number
when outputting a component error in OpVectorShuffle. The error line
isn't the best at this point as it points at the component, but it's
better then a -1 (turning to max<size_t>) that was being output.
The error messages has been updated to better reflect what the error is
attempting to say.
Issue 1719.
- Vulkan 1.0 uses strict layout rules
- Vulkan 1.0 with relaxed-block-layout validator option
enforces all rules except for the relaxation of vector
offset.
- Vulkan 1.1 and later always supports relaxed block layout
Add spot check tests for the relaxed-block-layout scenarios.
Fixes#1697
This CL moves the various validate files into the val/ directory with
the rest of the validation infrastructure. This matches how opt/ is
setup with the passes with the infrastructure.
Other environments do not.
Add tests for OpenGL 4.5 and SPIR-V universal 1.0 to ensure
they still check monotonic layout.
For universal 1.0, we're assuming it otherwise follows Vulkan
rules for block layout.
Fixes#1685
This CL moves the validation code to the val:: namespace. This makes it
clearer which instance of the Instruction and other classes are being
referred too.
Implement rules for row-major matrices
Use ArrayStride and MatrixStride to compute sizes
Propagate matrix stride and RowMajor/ColumnMajor through array members of structs.
Fixes#1637Fixes#1668
Fixes#1618.
Adds a check that validates acceptable exits from case constructs. Case
constructs may only exit to another case construct, the corresponding
merge, an outer loop continue or outer loop merge.
Fixes#1664 : PushConstant with Block follows storage buffer rules
PushConstant variables were being checked with block rules, which are
too strict.
Fixes#1606 : StorageBuffer with Block layout follows buffer rules
StorageBuffer variables were not being checked before.
Fix layout messages: say storage class and decoration
We need to provide more information about storage class and decoration.
- Add asm/dis test for SPV_KHR_8bit_storage
- validator: SPV_KHR_8bit_storage capabilities enable declaration of 8bit int
TODO:
- validator: ban arithmetic on 8bit unless Int8 is enabled
Covered by https://github.com/KhronosGroup/SPIRV-Tools/issues/1595
Produce better error diagnostics in the CFG validation.
This CL fixes up several issues with the diagnostic error line output
in the CFG validation code. For the cases where we can determine a
better line it has been output. For other cases, we removed the
diagnostic line and the error line number from the results.
Fixes#1657
Fixes#937
Stop std140/430 validation when runtime array is encountered.
Check for standard uniform/storage buffer layout instead of std140/430.
Added validator command line switch to skip block layout checking.
Validate structs decorated as Block/BufferBlock only when they
are used as variable with storage class of uniform or push
constant.
Expose --relax-block-layout to command line.
dneto0 modification:
- Use integer arithmetic instead of floor.
We need this to reduce the test time on Visual Studio debug builds.
AppVeyor times out at 300s for a process.
Artificially lower the local variable limit check for testing purposes.
We don't get much value from using the full 500K+ variables.
Use a limit of 5000 instead.
Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/1632
Add SPV_ENV_WEBGPU_0 for work-in-progress WebGPU.
val: Disallow OpUndef in WebGPU env
Silence unused variable warnings when !defined(SPIRV_EFFCE)
Limit visibility of validate_instruction.cpp's symbols
Only InstructionPass needs to be visible so all other functions are put
in an anonymous namespace inside the libspirv namespace.
Also add a corresponding check for capabilities in the validator.
Update previously existing test cases where an instruction used to fail
assembling because of a version check, but now they succeed because the
instruction is also guarded by a capability. Now it should assemble.
Add tests to ensure that capabilities are checked appropriately.
The explicitly reserved instructions OpImageSparseSampleProj*
now assemble, but they fail validation.
Fixes#1624
[val] Add extra context to error messages.
This CL extends the error messages produced by the validator to output the
disassembly of the errored line.
The validation_id messages have also been updated to print the line number of
the error instead of the word number. Note, the error number is from the start
of the SPIR-V, it does not include any headers printed in the disassembled code.
Fixes#670, #1581
This CL reverts the revert of 'Disallow array-of-arrays with DescriptorSets when
validating." Other changes have been committed which should aleviate the
AppVeryor resource constraints.
This reverts commit f2c93c6e12.
This CL adds validation to disallow using an array-of-arrays when attached to a
DescriptorSet.
Fixes#1522
Validate Ids before DataRules.
The DataRule validators call FindDefs with the assumption that they
definitions being looked at can be found. This may not be true if we
have not validated identifiers first.
This CL flips the IdPass and DataRulesPass to fix this issue.
Fixes#491
* Basic blocks now have a link to the terminator
* Check all case sepecific rules
* Missing check for branching into the middle of a case (#1618)
Fixes#1120
Checks that all static uses of the Input and Output variables are listed
as interfaces in each corresponding entry point declaration.
* Changed validation state to track interface lists
* updated many tests
* Modified validation state to store entry point names
* Combined with interface list and called EntryPointDescription
* Updated uses
* Changed interface validation error messages to output entry point name
in addtion to ID
Try to reduce the amount of disk space used by especially by debug builds,
which may be contributing to AppVeyor failures.
Collapses tests in categories:
- validator
- loop optimizations
- dominator analysis
- linker
Contributes to #1615
- Fix tests for basic group operations (e.g. Reduce) to allow for
new capabilities in SPIR-V 1.3 that enable them.
- Refactor operand capability check to avoid code duplication and
to put all checks that don't need table lookup before any table
lookup.
- Test round trip assembly/disassembly support for extension
SPV_NV_viewport_array2
- Test assembly and validation of decoration ViewportRelativeNV
Fixes#1596
Fixes#1281
* New structured cfg check: all non-construct header blocks'
predecessors must come from within the construct
* New function to calculate blocks in a construct
* Fixed a bug in BasicBlock type bitset
Relaxing check to not consider unreachable predecessors
* Fixing broken common uniform elim test
This CL updates the validate_id code to output the name of the object along with
the id number. There were a few instances which already output the name, this
just extends to all of them. Now, the output should say 123[obj] instead of just
123.
Issue #1581
* Disallow array-of-arrays with DescriptorSets when validating.
This CL adds validation to disallow using an array-of-arrays when attached to a
DescriptorSet.
Fixes#1522
According to the SPIR-V Spec, section 2.4 Logical Layout of a Module there
should be a single required OpMemoryModel instruction provided. This CL adds
validation that OpMemoryModel is provided to the SPIR-V validator.
Fixes#1207
SPV_EXT_shader_viewport_index_layer enables using ViewportIndex
and Layer in vertex and tessellation shaders.
Also, as per the Vulkan spec:
> The ViewportIndex decoration must be used only within vertex,
> tessellation evaluation, geometry, and fragment shaders.
> In a vertex, tessellation evaluation, or geometry shader, any
> variable decorated with ViewportIndex must be declared using
> the Output storage class.
> In a fragment shader, any variable decorated with ViewportIndex
> must be declared using the Input storage class.
Similarly for Layer.
* Adds new pass for validating non-uniform group instructions
* Currently on checks execution scope for Vulkan 1.1 and SPIR-V 1.3
* Added test framework
* Reworked how execution model limitations are checked
* Now OpFunction checks which entry points call it and checks its
registered limitations instead of building a call stack in the entry
point
* New tests
* Moving function to entry point mapping into VState
Relaxs checks for per-vertex builtin variables. If the builtin
decoration is applied to a variable, then those checks now allow a level
of arraying on the variable before checking the type consistency.
* Allows arrays of variables to be present for the per-vertex variables:
* Position
* PointSize
* ClipDistance
* CullDistance
* Updated tests
Add test for case where OpBranch branches to a value (a function value).
Previous tests only checked a label value (name of a block.).
Update validate_id.cpp to remove the TODO for OpBranch and say that it
is already checked in validate_cfg.cpp
According to Vulkan spec 1.1.72:
> The PrimitiveId decoration must be used only within fragment,
> tessellation control, tessellation evaluation, and geometry shaders.
> In a tessellation control or tessellation evaluation shader, any
> variable decorated with PrimitiveId must be declared using the Input
> storage class.
We were enforcing that PrimitiveId can only be used with Output
storage class for TCS and TES before.
Update grammar table generation:
- Get extensions from instructions, not just operand-kinds
- Don't explicitly list extensions that come from the SPIR-V core
grammar or from a KHR extended instruction set grammar.
This makes it easier to support new extensions since the recommended
extension strategy is to add instructions to the core grammar file.
Also, test the validator has trivial support for passing through
the extensions SPV_NV_shader_subgroup_partitioned and
SPV_EXT_descriptor_indexing.
Migrating to unified grammar means we sometimes have two fields
for a certain feature: version and extensions. It means the feature
in question can be used either in SPIR-V of advanced-enough
versions or in any SPIR-V with with the specified extensions.
Validator now respects the above rules.
At every definition of a builtin id, run at-reference-check rules on the
defining instruction as well.
Previosly the validation was missing the case when invalid storage class
was defined in the instruction which defines the built-in, and not in
the instruction which references the built-in.
Refactored validate built-ins to make
GetExecutionModels(entry_point)
and
GetExecutionModes(entry_point)
available in validation state.
Entry points are allowed to have multiple execution modes and execution
models.
Finished the last missing feature in Vulkan built-ins validation:
FragDepth requires DepthReplacing.
Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/1427
Adjusting validation to the new rule:
"Before version 1.3, it is only valid to use this instruction with
TessellationControl, GLCompute, or Kernel execution models.
There is no such restriction starting with version 1.3."
Also fixed wrong version numbers in source/spirv_target_env.cpp.
Added a framework for validation of BuiltIn variables. The framework
allows implementation of flexible abstract rules which are required for
built-ins as the information (decoration, definition, reference) is not
in one place, but is scattered all over the module.
Validation rules are implemented as a map
id -> list<functor(instrution)>
Ids which are dependent on built-in types or objects receive a task
list, such as "this id cannot be referenced from function which is
called from entry point with execution model X; propagate this rule
to your descendants in the global scope".
Also refactored test/val/val_fixtures.
All built-ins covered by tests
Previously we keep a separate static grammar table for opcodes/
operands per SPIR-V version. This commit changes that to use a
single unified static grammar table for opcodes/operands.
This essentially changes how grammar facts are queried against
a certain target environment. There are only limited filtering
according to the desired target environment; a symbol is
considered as available as long as:
1. The target environment satisfies the minimal requirement of
the symbol; or
2. There is at least one extension enabling this symbol.
Note that the second rule assumes the extension enabling the
symbol is indeed requested in the SPIR-V code; checking that
should be the validator's work.
Also fixed a few grammar related issues:
* Rounding mode capability requirements are moved to client APIs.
* Reserved symbols not available in any extension is no longer
recognized by assembler.
As per Vulkan spec, BuiltIn variables can't have Location or Component
decorations. On some drivers, these can lead to driver crashing when
compiling the shader pipeline; for example, NVidia/AMD desktop drivers:
https://github.com/KhronosGroup/glslang/issues/1182.
This change adds validation and tests to catch this.
Ban floating point case for OpAtomicLoad, OpAtomicExchange,
OpAtomicCompareExchange. In graphics (Shader) environments, these
instructions only operate on scalar integers. Ban the floating point
case. OpenCL supports atomic_float.
Implemented Vulkan-specific rules:
- OpTypeImage must declare a scalar 32-bit float or 32-bit integer type
for the “Sampled Type”.
- OpSampledImage must only consume an “Image” operand whose type has its
“Sampled” operand set to 1.
In HLSL structured buffer legalization, pointer to pointer types
are emitted to indicate a structured buffer variable should be
treated as an alias of some other variable. We need an option to
relax the check of pointer types in logical addressing mode to
catch other validation errors.
1. Added OpCompositeExtract/Insert out of bounds checks where possible
(everything except RuntimeArray)
2. Moved validation of OpCompositeExtract/Insert from validate_id.cpp to
validate_composites.cpp.
- Test validation success for OpEmitVertex OpEndPrimitive
- Test missing capabilities for primitive instructions
- Primitive instructions require Geometry execution model
@ehsannas had filed an issue against SPIR-V spec, concerning
Image Operands section (3.14):
Sample
A following operand is the sample number of the sample to use. Only
valid with OpImageFetch, OpImageRead, and OpImageWrite.
Relaxing the check to allow OpImageSparseRead and
OpImageSparseFetch to fix failing tests.
include: Add target environment enums for OpenCL 1.2 and 2.0
Validator: Validate OpenCL capabilities
Update validate capabilities to handle embedded profiles
Add test for OpenCL capabilities validation
Update messages to mention the OpenCL profile used
Re-format val_capability_test.cpp
This needs custom code since the rules from the extension
are not encoded in the grammar.
Changes are:
- The new group instructions don't require Group capability
when the extension is declared.
- The Reduce, InclusiveScan, ExclusiveScan normally require the Kernel
capability, but don't when the extension is declared.
Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/991
Re-formatted the source tree with the command:
$ /usr/bin/clang-format -style=file -i \
$(find include source tools test utils -name '*.cpp' -or -name '*.h')
This required a fix to source/val/decoration.h. It was not including
spirv.h, which broke builds when the #include headers were re-ordered by
clang-format.
Removed the check that result type of OpImageRead should be a vector4.
Will reenable/adapt once the spec is clarified on what the right
dimension should be.
There are a number of users of spriv-opt that are hitting errors
because of stores with different types. In general, this is wrong, but,
in these cases, the types are the exact same except for decorations.
The options is "--relax-store-struct", and it can be used with the
validator or the optimizer.
We assume that if layout information is missing it is consistent. For
example if one struct has a offset of one of its members, and the other
one does not, we will still consider them as being layout compatible.
The problem will be if both struct has and offset decoration for
corresponding members, and the offset are different.
The pass checks correctness of operands of instruction in opcode range
OpConvertFToU - OpBitset.
Disabled invalid tests
Disabled UConvert validation until Vulkan CTS can catch up.
Add validate_conversion to Android.mk
Also remove duplicate entry in CMakeLists.txt.
Use the list from the SPIR-V registry page. Also, capture it as
a string so it's much easier to update via copy-paste.
The validator will accept modules that declare these known
extensions. However, we might not know about new tokens or
instructions declared in them. For that we need grammar updates
applied to SPIRV-Headers.
If the variable_pointer extension is used:
* OpLoad's pointer argument may be the result of any of the following:
* OpSelect
* OpPhi
* OpFunctionCall
* OpPtrAccessChain
* OpCopyObject
* OpLoad
* OpConstantNull
* Return value of a function may be a pointer.
* It is valid to use a pointer as the return value of a function.
* OpStore should allow a variable pointer argument.
Supported in assembler, disassembler, and binary parser.
The validator does not check SPV_AMD_gcn_shader validation rules
beyond parsing the extension.
Adds generic support for generating instruction tables for vendor
extensions.
Adds generic support for extensions the validator should recognize
(but not check) but which aren't derived from the SPIR-V core
grammar file.
Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/594
Autogenerating the following code:
- extension enum
- extension-to-string
- string-to-extension
- capability-to-string
Capability mapping table will not compile if incomplete.
TODO: Use "spirv-latest-version.h" instead of 1.1.
Added function to generate capability tables for tests.
Known extensions are saved in validation state. Unknown extension
produce a dignostic message, but do not fail the validation.
Moved extension definitions to their own file.
The assembler assigns ID numbers sequentially, so it's confusing
to have a %1 in the source assembly when it isn't the first mentioned
ID. Rewrite the ID names to avoid this situation in a few cases.
From the SPIR-V Spec 2.16.1:
A function declaration (an OpFunction with no basic blocks), must have
a Linkage Attributes Decoration with the Import Linkage Type.
A function definition (an OpFunction with basic blocks) cannot be
decorated with the Import Linkage Type.
The limit for the number of struct members is parameterized using
command line options.
Add --max-struct-depth command line option.
Add --max-switch-branches command line option.
Add --max-function-args command line option.
Add --max-control-flow-nesting-depth option.
Add --max-access-chain-indexes option.
If a merge block is reachable, then it must be *strictly* dominated
by its header. Until now we've allowed the header and the merge
block to be the same.
Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/551
Also: Use dominates and postdominates methods on BasicBlock to
improve readability.
It is best to check the error messages of unit tests that fail
validation. This will ensure that a validation failure is due to what we
expect and not due to some secondary reason.
Updating SPIR-V Validator unit tests with error message checks.
When applied to a structure-type member, all members of that structure
type must also be decorated with BuiltIn. (No allowed mixing of built-in
variables and non-built-in variables within a single structure.)
When applied to a structure-type member, that structure type cannot be
contained as a member of another structure type.
There is at most one object per Storage Class that can contain a
structure type containing members decorated with BuiltIn, consumed per
entry-point.
It is acceptable for OpAccessChain, OpInBoundsAccessChain,
OpPtrAccessChain, OpInBoundsPtrAccessChain, OpCompositeInsert, and
OpCompositeExtract to not take any indexes as arguments. In such cases,
no indexing will be done on the Base pointer/composite.
Added a new file where all the decoration validation can be performed.
In this change the SPIRV Spec Section 2.16.1 is implemented:
"It is illegal to initialize an imported variable. This means
that a module-scope OpVariable with initialization value cannot be
marked with the Import Linkage Type."
Also added unit tests.
* Added the decoration class as well as the code that registers the
decorations for each <id> and also decorations for struct members.
* Added unit tests for decorations in ValidationState as well as
decoration id tests.
According to the SPIRV Spec (2.16.1):
* There is at least one OpEntryPoint instruction, unless the Linkage
capability is being used.
* No function can be targeted by both an OpEntryPoint instruction and an
OpFunctionCall instruction.
Also updated unit tests to includ OpEntryPoint.
We are adding a new API which can be called to run the SPIR-V validator,
and retrieve the ValidationState_t object. This is very useful for
unit testing.
I have also added basic unit tests that demonstrate usage of this flow
and ease of use to verify correctness.
The validity of each command is checked based on the descripton in
SPIR-V Spec Section 3.32.12 (Composite Instructions).
Also checked that the number of indexes passed to these commands does
not exceed the limit described in 2.17 (Universal Limits).
Also added unit tests for each one.
entry_block_to_construct_ maps an entry block to its construct. The key
in this map (the entry block) is not unique, and therefore the entry for
the continue construct gets overwritten when the selection construct is
discovered.
Since a given block may be the entry block of different types of
constructs, the (basic_block, construct_type) pair should be able to
uniquely identify the construct.
Adds test:
- In this test, a basic block is the entry block of a continue construct
as well as the entry block of a selection construct.
It can be shown that this unit test would crash without the fix in this
PR and passes with the fix in this PR.
Validation for OpPtrAccessChain is similar to OpAccessChain with the
following difference: OpPtrAccessChain takes an extra argument (word 4)
which is the Element <id> argument.
Validation for OpInBoundsPtrAccessChain is also similar to OpPtrAccessChain.
Also added tests for all access chain instructions:
Modified the existing parameterized tests to accommodate OpPtrAccessChain and
OpInBoundsPtrAccessChain.
Also fixed a typo in previous commits.
Using parameterized unit tests to avoid duplicate code that runs the
tests of OpAccessChain and OpInBoundsAccessChain.
This is also a steppingstone to adding tests for OpPtrAccessChain and
OpInBoundsPtrAccessChain.
According to Section 2.17 (Universal Limits) of the SPIR-V Spec, the
control flow nesting depth may not be larger than 1023.
This is checked only when we are required to have structured
control flow. Otherwise it's not clear how to compute control
flow nesting depth.
According to sectin 2.17 in SPIR-V Spec, the structure nesting depth may
not be larger than 255. This is interpreted as structures nested in
structures. The code does not look into arrays or follow pointers to see
if it reaches a structure downstream.
Use memoization to avoid exponential runtime.
The validation code for OpAccessChain was missing OpTypeRuntimeArray as
a possible type that can be indexed into.
This was caught by running the validator on VKCTS.
Also adding unit tests for it.
* Result Type must be an OpTypePointer. Its Type operand must be the
type reached by walking the Base’s type hierarchy down to the last
provided index in Indexes, and its Storage Class operand must be the
same as the Storage Class of Base.
* Base must be a pointer, pointing to the base of a composite object.
* Indexes walk the type hierarchy to the desired depth, potentially down
to scalar granularity. The first index in Indexes will select the
top-level member/element/component/element of the base composite. All
composite constituents use zero-based numbering, as described by their
OpType... instruction. The second index will apply similarly to that
result, and so on. Once any non-composite type is reached, there must
be no remaining (unused) indexes. Each of the Indexes must:
- be a scalar integer type,
- be an OpConstant when indexing into a structure.
* Check for the case where no indexes are passed to OpAccessChain.
Minor improvements based on code review.
According to the Universal Limits section of the SPIR-V Spec (2.17), the
number of global variables may not exceed 65,535 and the number of local
variables may not exceed 524,287.
Also added unit tests for each one.
According to the SPIR-V spec (section 2.17: Universal Limits), the
OpTypeFunction instruction may not take more than 255 arguments for the
function. Also added unit tests for it.
The number of (literal, label) pairs passed to OpSwitch may not exceed
16,383. Added code to validate this and added unit tests for it.
Also fixed a typo in another validor error message.
This is described in Section 2.17 of the SPIR-V Spec.
* Updated existing unit test 'SemanticsIdIsAnIdNotALiteral' to pass by
manipulating the ID bound in its binary header.
* Fixed boundary check in the code.
* Added unit test to check the case that the largest ID is equal to the
ID bound.
This change implements the validation for usages of OpSampledImage
instruction as described in the Data Rules section of the Universal
Validation Rules of the SPIR-V Spec.
SpecConstantComposite may specialize to a vector, matrix, array, or
struct. In each case, the number of components and type of components
that are being specialized to must match the expected result type.
Removed use of macros in these tests.
Now using the spvValidateBase class. Using CompileSuccessfully(), and
ValidateInstructions() to compile to binary and run the validator. Also
using getDiagnosticString() to check the proper error message string.
All the heavy lifting is done in ValidateBase class.
According to the Data Rules section of 2.16.1. Universal Validation
Rules of the SPIR-V Spec:
Forward reference operands in an OpTypeStruct
* must be later declared with OpTypePointer
* the type pointed to must be an OpTypeStruct
* had an earlier OpTypeForwardPointer forward reference to the same <id>
These rules are under "Data Rules" in 2.16.1 (Universal Validation
Rules) part of the SPIR-V 1.1 Specification document:
* Scalar floating-point types can be parameterized only as 32 bit, plus
any additional sizes enabled by capabilities.
* Scalar integer types can be parameterized only as 32 bit, plus any
additional sizes enabled by capabilities.
* Vector types can only be parameterized with numerical types or the
OpTypeBool type.
* Matrix types can only be parameterized with floating-point types.
* Matrix types can only be parameterized as having only 2, 3, or 4
columns.
* Specialization constants (see Specialization) are limited to integers,
Booleans, floating-point numbers, and vectors of these.
Number of components in a vector can be 2 or 3 or 4. If Vector16
capability is used, 8 and 16 components are also allowed.
Also added unit tests for vector data rule.
* Allows OpTypeForwardPointer to reference IDs not yet declared in
the module
* Allows OpTypeStruct to reference IDs not yet declared in
the module
Possible Issue: OpTypeStruct should only allow forward references
if the ID is a pointer that is referenced by a forward pointer. Need
Type support in Validator which is currently a work in progress.
Every time an event happens in the library that the user should be
aware of, the callback will be invoked.
The existing diagnostic mechanism is hijacked internally by a
callback that creates an diagnostic object each time an event
happens.
Defer removal of a Phi's result id from the undefined-forward-reference
set until after you've scanned the arguments. The reordering is only
significant for Phi.
Fixes https://github.com/KhronosGroup/SPIRV-Tools/issues/415
