spirv-opt has a bug that `DebugInfoManager::AddDebugValueWithIndex()` does not
preserve `Indexes` operands of
[DebugValue](https://www.khronos.org/registry/spir-v/specs/unified1/OpenCL.DebugInfo.100.html#DebugValue).
It has to preserve all of those `Indexes` operands, but it preserves only the first index
operand.
This PR removes `DebugInfoManager::AddDebugValueWithIndex()` and lets the spirv-opt
use `DebugInfoManager::AddDebugValueForDecl()`.
`DebugInfoManager::AddDebugValueForDecl()` preserves the Indexes operand correctly.
The front-end language compiler would simply emit DebugDeclare for
a variable when it is declared, which is effective through the variable's
scope. Since DebugDeclare only maps an OpVariable to a local variable,
the information can be removed when an optimization pass uses the
loaded value of the variable. DebugValue can be used to specify the
value of a variable. For each value update or phi instruction of a variable,
we can add DebugValue to help debugger inspect the variable at any
point of the program execution.
For example,
float a = 3;
... (complicated cfg) ...
foo(a); // <-- variable inspection: debugger can find DebugValue of `float a` in the nearest dominant
For the code with complicated CFG e.g., for-loop, if-statement, we
need help of ssa-rewrite to analyze the effective value of each variable
in each basic block.
If the value update of the variable happens only once and it dominates
all its uses, local-single-store-elim pass conducts the same value update
with ssa-rewrite and we have to let it add DebugValue for the value assignment.
One main issue is that we have to add DebugValue only when the value
update of a variable is visible to DebugDeclare. For example,
```
{ // scope1
%stack = OpVariable %ptr_int %int_3
{ // scope2
DebugDeclare %foo %stack <-- local variable "foo" in high-level language source code is declared as OpVariable "%stack"
// add DebugValue "foo = 3"
...
Store %stack %int_7 <-- foo = 7, add DebugValue "foo = 7"
...
// debugger can inspect the value of "foo"
}
Store %stack %int_11 <-- out of "scope2" i.e., scope of "foo". DO NOT add DebugValue "foo = 11"
}
```
However, the initalization of a variable is an exception.
For example, an argument passing of an inlined function must be done out of
the function's scope, but we must add a DebugValue for it.
```
// in HLSL
bar(float arg) { ... }
...
float foo = 3;
bar(foo);
// in SPIR-V
%arg = OpVariable
OpStore %arg %foo <-- Argument passing. Out of "float arg" scope, but we must add DebugValue for "float arg"
... body of function bar(float arg) ...
```
This PR handles the except case in local-single-store-elim pass. It adds
DebugValue for a store that is considered as an initialization.
The same exception handling code for ssa-rewrite is done by this commit: df4198e50e.
For some cases, we have DebugDecl invisible to a value assignment, but
the value assignment information is important i.e., debugger cannot inspect
the variable without the information. For example, a parameter of an inlined
function must have its value assignment i.e., argument passing out of its
function scope. If we simply remove DebugDecl because it is invisible to the
argument passing, we cannot inspec the variable.
This PR
- Adds DebugValue for DebugDecl invisible to a value assignment. We use
the value of the variable in the basic block that contains DebugDecl, which is
found by ssa-rewrite. If the value instruction does not dominate DebugDecl,
we use the value of the variable in the immediate dominator of the basic block.
- Checks the visibility of DebugDecl for Phi value assignment based on the
all value operands of the Phi. Since Phi just references multiple values from
multiple basic blocks, scopes of value operands must be regarded as the scope
of the Phi.
`DebugInfoManager::AddDebugValueIfVarDeclIsVisible()` adds
OpenCL.DebugInfo.100 DebugValue from DebugDeclare only when the
DebugDeclare is visible to the give scope. It helps us correctly
handle a reference variable e.g.,
{ // scope #1.
int foo = /* init */;
{ // scope #2.
int& bar = foo;
...
in the above code, we must not propagate DebugValue of `int& bar` for
store instructions in the scope #1 because it is alive only in
the scope #2.
We have an exception: If the given DebugDeclare is used for a function
parameter, `DebugInfoManager::AddDebugValueIfVarDeclIsVisible()` has
to always add DebugValue instruction regardless
of the scope. It is because the initializer (store instruction) for
the function parameter can be out of the function parameter's scope
(the function) in particular when the function was inlined.
Without this change, the function parameter value information always
disappears whenever we run the function inlining pass and
`DebugInfoManager::AddDebugValueIfVarDeclIsVisible()`.
When we update OpenCL.DebugInfo.100 lexical scopes e.g., DebugFunction,
we have to replace DebugScope of each instruction that uses the lexical
scope correctly.
When we copy the loop body to unroll it, we have to copy its
instructions but DebugDeclare or DebugValue used for the declaration
i.e., DebugValue with Deref must not be copied and only the first block
can contain those instructions.
1. Set the debug scope and line information for the new replacement
instructions.
2. Replace DebugDeclare and DebugValue if their OpVariable or value
operands are replaced by scalars. It uses 'Indexes' operand of
DebugValue. For example,
struct S { int a; int b;}
S foo; // before scalar replacement
int foo_a; // after scalar replacement
int foo_b;
DebugDeclare %dbg_foo %foo %null_expr // before
DebugValue %dbg_foo %foo_a %Deref_expr 0 // after
DebugValue %dbg_foo %foo_b %Deref_expr 1 // means Value(foo.members[1]) == Deref(%foo_b)
Essentially, it marks all DebugInfo instructions in functions (and their operands) as live. It treats DebugDeclare and DebugValue with Deref as loads and so marks Stores of their variables as live.
It marks each DebugGlobalVariables as live except for its variable. After closure, it rechecks if the variable is live. If not, the DebugGlobalVariable instruction's variable operand is set to DebugInfoNone, per the DebugInfo spec.
This pass basically follows the same process as ssa-rewrite: it adds a DebugValue after each Store and removes the DebugDeclare or DebugValue Deref. It only does this if all instructions that are dependent on the Store are Loads and are replaced.
When the pass replaces the local variable `OpVariable` ids to their
corresponding pointers, we have to update operands of DebugValue or
DebugDeclare instructions.
For many spirv-opt passes such as simplify-instructions pass, we have to
correctly clear the OpenCL.DebugInfo.100 debug information for
KillInst() and ReplaceAllUses(). If we keep some debug information that
disappeared because of KillInst() and ReplaceAllUses(), adding new
DebugValue instructions based on the existing DebugDeclare information
will generate incorrect information. This CL update DebugInfoManager
and IRContext to correctly clear debug information.
Add OpenCL.DebugInfo.100 `DebugValue` instructions for store
and phi instructions of local variables to provide the debugger with
the updated values of local variables correctly.
Handles the OpenCL100Debug extension in inlining. It preserves the information that is available while also adding the debug inlined at for all of the inlining that it does.
We need an analysis for OpenCL.DebugInfo.100 extension instructions such
as a map between function id and its DebugFunction. This commit add an
analysis for it.
