[llvm] [AArch64] Sub, add, and icmp should have the fact they can be negated in the cost (PR #142844)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: AZero13 (AZero13)

<details>
<summary>Changes</summary>



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


1 Files Affected:

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


``````````diff
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;

``````````

</details>


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