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The code changes look mostly OK to me. The test changes also look OK right now at first reading, although it is a bit new for me to see a three pass opt pipeline instead of using -O1 in clang, but I see that it does demonstrate hoisting. I approved CI tests, so, I will await those results, and I'm curious about the performance impact of this change in the default pipeline. |
schittir
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Sep 16, 2026
| // A builtin with no side effects cannot trap and always | ||
| // returns, so it is safe to speculate. Without this, licm | ||
| // cannot hoist a call to it out of a conditional block. | ||
| if (Builtin.IsConst) { |
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Is IsConst the right/precise enough check to add these attributes?
A SPIR-V builtin declared Attr.Const computes its result from its arguments alone, but clang only gives it memory(none) and willreturn. LLVM needs speculatable before it will move a call out of a conditional block, so licm cannot hoist such a call out of a loop. Mark those declarations speculatable and not convergent. The attribute goes on the declaration alone: a call site may carry speculatable only while its callee carries it too, which stops holding once a module that defines the builtin, such as libclc, is linked in.
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| @@ -0,0 +1,22 @@ | |||
| // RUN: %clang_cc1 -triple spir64 -fdeclare-spirv-builtins -fconvergent-functions \ | |||
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This should not be a FE test. The FileCheck is testing a pass (?) output, not what the FE is emitting. This should be moved wherever the pass is tested.
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A SPIR-V builtin declared Attr.Const computes its result from its arguments alone, but clang only gives it memory(none) and willreturn. LLVM needs speculatable before it will move a call out of a conditional block, so licm cannot hoist such a call out of a loop. Mark those declarations speculatable and not convergent.