[PATCH] D156499: [InstCombine] Fold abs of known sign operand when source is sub

[Allen zhong via Phabricator via llvm-commits]

Allen updated this revision to Diff 545095.
Allen edited the summary of this revision.
Allen added a comment.

address comment, **move the transform out of the getKnownSign** to avoid breaking the perspective of the getKnownSign() API


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D156499/new/

https://reviews.llvm.org/D156499

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
  llvm/test/Transforms/InstCombine/abs-intrinsic.ll


Index: llvm/test/Transforms/InstCombine/abs-intrinsic.ll
===================================================================
--- llvm/test/Transforms/InstCombine/abs-intrinsic.ll
+++ llvm/test/Transforms/InstCombine/abs-intrinsic.ll
@@ -512,11 +512,10 @@
 ; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp sgt i32 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP_NOT]], label [[COND_END:%.*]], label [[COND_TRUE:%.*]]
 ; CHECK:       cond.true:
-; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 true)
+; CHECK-NEXT:    [[SUB_NEG:%.*]] = sub i32 [[Y]], [[X]]
 ; CHECK-NEXT:    br label [[COND_END]]
 ; CHECK:       cond.end:
-; CHECK-NEXT:    [[R:%.*]] = phi i32 [ [[TMP0]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[R:%.*]] = phi i32 [ [[SUB_NEG]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
 entry:
Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1530,8 +1530,19 @@
     if (match(IIOperand, m_Select(m_Value(), m_Neg(m_Value(X)), m_Deferred(X))))
       return replaceOperand(*II, 0, X);
 
+    // abs(x-y) --> y-x where x <= y
+    Value *Y;
+    if (match(IIOperand, m_NSWSub(m_Value(X), m_Value(Y)))) {
+      if (std::optional<bool> Known =
+              isImpliedByDomCondition(ICmpInst::ICMP_SLE, X, Y, II, DL)) {
+        if (!*Known)
+          return replaceInstUsesWith(*II, IIOperand);
+        return BinaryOperator::CreateNeg(IIOperand);
+      }
+    }
+
     if (std::optional<bool> Sign = getKnownSign(IIOperand, II, DL, &AC, &DT)) {
-      // abs(x) -> x if x >= 0
+      // abs(x) -> x if x >= 0 (include abs(x-y) --> x-y where x >= y)
       if (!*Sign)
         return replaceInstUsesWith(*II, IIOperand);
 


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