[AArch64] Fix a presumed typo in isFPImmLegal limit. NFC#106716
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[AArch64] Fix a presumed typo in isFPImmLegal limit. NFC#106716
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The worst possible case for a double literal goes like: ``` mov ... movk ..., lsl llvm#16 movk ..., lsl llvm#32 movk ..., lsl llvm#48 fmov ... ``` The limit of 5 in the code gives the impression that `Insn` includes all instructions including the `fmov`, but that's not true. It only counts the integer moves. This led me astray on some other work in this area.
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@llvm/pr-subscribers-backend-aarch64 Author: Marina Taylor (citymarina) ChangesThe worst possible case for a double literal goes like: The limit of 5 in the code gives the impression that Full diff: https://github.com/llvm/llvm-project/pull/106716.diff 1 Files Affected:
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 02390e0a85c0a5..98f6f30112a8c7 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -11463,7 +11463,8 @@ bool AArch64TargetLowering::isFPImmLegal(const APFloat &Imm, EVT VT,
// movw+movk is fused). So we limit up to 2 instrdduction at most.
SmallVector<AArch64_IMM::ImmInsnModel, 4> Insn;
AArch64_IMM::expandMOVImm(ImmInt.getZExtValue(), VT.getSizeInBits(), Insn);
- unsigned Limit = (OptForSize ? 1 : (Subtarget->hasFuseLiterals() ? 5 : 2));
+ assert(Insn.size() <= 4);
+ unsigned Limit = (OptForSize ? 1 : (Subtarget->hasFuseLiterals() ? 4 : 2));
IsLegal = Insn.size() <= Limit;
}
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Aug 30, 2024
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Aug 30, 2024
| @@ -11463,7 +11463,9 @@ bool AArch64TargetLowering::isFPImmLegal(const APFloat &Imm, EVT VT, | |||
| // movw+movk is fused). So we limit up to 2 instrdduction at most. | |||
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Do you mind changing instrdduction to instructions whilst you are here?
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Oh - you remove it in a follow up. Don't worry about it here then.
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The worst possible case for a double literal goes like:
The limit of 5 in the code gives the impression that
Insnincludes all instructions including thefmov, but that's not true. It only counts the integer moves. This led me astray on some other work in this area.