[AArch64] Sub, add, and icmp should have the fact they can be negated in the cost

[AZero13]

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[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: AZero13 (AZero13)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/142844.diff

1 Files Affected:

• (modified) llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp (+7-1)

diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index 68aec80f07e1d..542b34df8b345 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -473,7 +473,13 @@ InstructionCost AArch64TTIImpl::getIntImmCostInst(unsigned Opcode, unsigned Idx,
 
   if (Idx == ImmIdx) {
     int NumConstants = (BitSize + 63) / 64;
-    InstructionCost Cost = AArch64TTIImpl::getIntImmCost(Imm, Ty, CostKind);
+    InstructionCost Cost;
+    if (Opcode == Instruction::Add || Opcode == Instruction::Sub ||
+        Opcode == Instruction::ICmp) {
+      // Add/Sub/ICmp immediates can be flipped.
+      Cost = AArch64TTIImpl::getIntImmCost(Imm.abs(), Ty, CostKind);
+    } else
+      Cost = AArch64TTIImpl::getIntImmCost(Imm, Ty, CostKind);
     return (Cost <= NumConstants * TTI::TCC_Basic)
                ? static_cast<int>(TTI::TCC_Free)
                : Cost;

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