Improve compare-and-branch sequences produced by Emitter #111797
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Introduces an overload of `genJumpToThrowHlpBlk` that allows you to pass a function that generates the branch code, before it creates an inline throw block. This allows us to choose compare-and-branch sequences such as `cbz` on ARM64 for checks added in the emitter, such as divide-by-zero.
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Emit `cbz` instead of `cmp+b.ls` when checking bounds for an access to the 0 index of an array. It can only throw when `arrayLength == 0`. Fixes dotnet#42514
src/coreclr/jit/codegencommon.cpp
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| BasicBlock* CodeGen::genGetThrowHelper(SpecialCodeKind codeKind) | ||
| { | ||
| bool useThrowHlpBlk = compiler->fgUseThrowHelperBlocks(); | ||
| #if defined(UNIX_X86_ABI) |
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can we remove this s because it is mainly used for arm64. Perhaps move this code from codegencommon.cpp to codegenarm64.cpp?
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Yes, I'll do that.
| // For ARM64 we only expect equality comparisons. | ||
| assert((cond == GenCondition::EQ) || (cond == GenCondition::NE)); | ||
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| if (compareImm == 0) |
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this method is just called with compareImm == 0. Are you planning to use it for other scenarios as well?
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Yes I would try and use this helper anywhere I have an immediate and want to compare-and-branch as it would handle the instruction selection generally.
Maybe if we used it here it might emit tbnz sometimes for 2^n? Otherwise it just simplifies that block.
runtime/src/coreclr/jit/codegenarm64.cpp
Line 4177 in adf123c
Possibly another
cbz case:runtime/src/coreclr/jit/codegenarm64.cpp
Line 4319 in adf123c
Introduces an overload of
genJumpToThrowHlpBlkthat allows you to pass a function that generates the branch code, before it creates an inline throw block. This allows us to choose compare-and-branch sequences such ascbzon ARM64 for checks added in the emitter, such as divide-by-zero.Working towards #68028, I'll be looking into something similar for #42514 next using this helper I've added.