[llvm] [AArch64] Report icmp as free if it can be folded into ands (PR #143286)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: AZero13 (AZero13)

<details>
<summary>Changes</summary>

Since changing the backend to fold x >= 1 / x < 1 -> x > 0 / x <= 0 and x <= -1 / x > -1 -> x > 0 / x <= 0,  this should be reflected in the cost.

---
Full diff: https://github.com/llvm/llvm-project/pull/143286.diff


1 Files Affected:

- (modified) llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp (+15-6) 


``````````diff
diff --git a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
index 68aec80f07e1d..72b60eaa45b78 100644
--- a/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp
@@ -4346,14 +4346,23 @@ InstructionCost AArch64TTIImpl::getCmpSelInstrCost(
   }
 
   // Treat the icmp in icmp(and, 0) as free, as we can make use of ands.
-  // FIXME: This can apply to more conditions and add/sub if it can be shown to
-  // be profitable.
   if (ValTy->isIntegerTy() && ISD == ISD::SETCC && I &&
-      ICmpInst::isEquality(VecPred) &&
+      !CmpInst::isUnsigned(VecPred) &&
       TLI->isTypeLegal(TLI->getValueType(DL, ValTy)) &&
-      match(I->getOperand(1), m_Zero()) &&
-      match(I->getOperand(0), m_And(m_Value(), m_Value())))
-    return 0;
+      match(I->getOperand(0), m_And(m_Value(), m_Value()))) {
+    if (match(I->getOperand(1), m_Zero()))
+      return 0;
+
+    // x >= 1 / x < 1 -> x > 0 / x <= 0
+    if (match(I->getOperand(1), m_One()) &&
+        (VecPred == CmpInst::ICMP_SLT || VecPred == CmpInst::ICMP_SGE))
+      return 0;
+
+    // x <= -1 / x > -1 -> x > 0 / x <= 0
+    if (match(I->getOperand(1), m_AllOnes()) &&
+        (VecPred == CmpInst::ICMP_SLE || VecPred == CmpInst::ICMP_SGT))
+      return 0;
+  }
 
   // The base case handles scalable vectors fine for now, since it treats the
   // cost as 1 * legalization cost.

``````````

</details>


https://github.com/llvm/llvm-project/pull/143286