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Don't try to unroll loop with step count 0. (#4769)

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These loop are infinite loop, so there is no reason to unroll the loop.
Fixes #4711.
This commit is contained in:
Steven Perron 2022-04-11 10:21:15 -04:00 committed by GitHub
parent c1bb0b9415
commit 92c17edde7
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3 changed files with 40 additions and 1 deletions
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4
source/opt/loop_descriptor.cpp
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@ -754,6 +754,10 @@ bool Loop::FindNumberOfIterations(const Instruction* induction,
// |step_value| is NOT cleanly divisible then we add one to the sum.
int64_t Loop::GetIterations(SpvOp condition, int64_t condition_value,
int64_t init_value, int64_t step_value) const {
if (step_value == 0) {
return 0;
}
int64_t diff = 0;
switch (condition) {

3
source/opt/loop_descriptor.h
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@ -398,7 +398,8 @@ class Loop {
// Each different loop |condition| affects how we calculate the number of
// iterations using the |condition_value|, |init_value|, and |step_values| of
// the induction variable. This method will return the number of iterations in
// a loop with those values for a given |condition|.
// a loop with those values for a given |condition|. Returns 0 if the number
// of iterations could not be computed.
int64_t GetIterations(SpvOp condition, int64_t condition_value,
int64_t init_value, int64_t step_value) const;

34
test/opt/loop_optimizations/unroll_simple.cpp
View File

@ -3789,6 +3789,40 @@ TEST_F(PassClassTest, PartialUnrollWithPhiReferencesPhi) {
SinglePassRunAndMatch<PartialUnrollerTestPass<2>>(text, true);
}
TEST_F(PassClassTest, DontUnrollInfiteLoop) {
// This is an infinite loop that because the step is 0. We want to make sure
// the unroller does not try to unroll it.
const std::string text = R"(OpCapability Shader
%1 = OpExtInstImport "GLSL.std.450"
OpMemoryModel Logical GLSL450
OpEntryPoint Fragment %2 "main"
OpExecutionMode %2 OriginUpperLeft
%void = OpTypeVoid
%4 = OpTypeFunction %void
%int = OpTypeInt 32 1
%int_0 = OpConstant %int 0
%int_50 = OpConstant %int 50
%bool = OpTypeBool
%int_0_0 = OpConstant %int 0
%2 = OpFunction %void None %4
%10 = OpLabel
OpBranch %11
%11 = OpLabel
%12 = OpPhi %int %int_0 %10 %13 %14
%15 = OpSLessThan %bool %12 %int_50
OpLoopMerge %16 %14 Unroll
OpBranchConditional %15 %14 %16
%14 = OpLabel
%13 = OpIAdd %int %12 %int_0_0
OpBranch %11
%16 = OpLabel
OpReturn
OpFunctionEnd
)";
SinglePassRunAndCheck<LoopUnroller>(text, text, false);
}
} // namespace
} // namespace opt
} // namespace spvtools