[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 547467.
Allen marked an inline comment as done.
Allen added a comment.

Address comment, and a new helper function getKnownSignOrZero


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:
@@ -540,11 +539,10 @@
 ; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp sgt i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP_NOT]], label [[COND_END:%.*]], label [[COND_TRUE:%.*]]
 ; CHECK:       cond.true:
-; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call i8 @llvm.abs.i8(i8 [[SUB]], i1 false)
+; CHECK-NEXT:    [[SUB_NEG:%.*]] = sub i8 [[Y]], [[X]]
 ; CHECK-NEXT:    br label [[COND_END]]
 ; CHECK:       cond.end:
-; CHECK-NEXT:    [[R:%.*]] = phi i8 [ [[TMP0]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[R:%.*]] = phi i8 [ [[SUB_NEG]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
 entry:
@@ -567,11 +565,10 @@
 ; CHECK-NEXT:    [[CMP_NOT:%.*]] = icmp sgt i8 [[X:%.*]], [[Y:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP_NOT]], label [[COND_END:%.*]], label [[COND_TRUE:%.*]]
 ; CHECK:       cond.true:
-; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i8 [[X]], [[Y]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call i8 @llvm.abs.i8(i8 [[SUB]], i1 true)
+; CHECK-NEXT:    [[SUB_NEG:%.*]] = sub i8 [[Y]], [[X]]
 ; CHECK-NEXT:    br label [[COND_END]]
 ; CHECK:       cond.end:
-; CHECK-NEXT:    [[R:%.*]] = phi i8 [ [[TMP0]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[R:%.*]] = phi i8 [ [[SUB_NEG]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
 entry:
Index: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1018,6 +1018,18 @@
       ICmpInst::ICMP_SLT, Op, Constant::getNullValue(Op->getType()), CxtI, DL);
 }
 
+static std::optional<bool> getKnownSignOrZero(Value *Op, Instruction *CxtI,
+                                              const DataLayout &DL,
+                                              AssumptionCache *AC,
+                                              DominatorTree *DT) {
+  if (std::optional<bool> Sign = getKnownSign(Op, CxtI, DL, AC, DT))
+    return Sign;
+
+  Value *X, *Y;
+  if (match(Op, m_NSWSub(m_Value(X), m_Value(Y))))
+    return isImpliedByDomCondition(ICmpInst::ICMP_SLE, X, Y, CxtI, DL);
+}
+
 /// Return true if two values \p Op0 and \p Op1 are known to have the same sign.
 static bool signBitMustBeTheSame(Value *Op0, Value *Op1, Instruction *CxtI,
                                  const DataLayout &DL, AssumptionCache *AC,
@@ -1518,12 +1530,15 @@
     if (match(IIOperand, m_Select(m_Value(), m_Neg(m_Value(X)), m_Deferred(X))))
       return replaceOperand(*II, 0, X);
 
-    if (std::optional<bool> Sign = getKnownSign(IIOperand, II, DL, &AC, &DT)) {
-      // abs(x) -> x if x >= 0
-      if (!*Sign)
+    if (std::optional<bool> Known =
+            getKnownSignOrZero(IIOperand, II, DL, &AC, &DT)) {
+      // abs(x) -> x if x >= 0 (include abs(x-y) --> x - y where x >= y)
+      // abs(x) -> x if x > 0 (include abs(x-y) --> x - y where x > y)
+      if (!*Known)
         return replaceInstUsesWith(*II, IIOperand);
 
       // abs(x) -> -x if x < 0
+      // abs(x) -> -x if x < = 0 (include abs(x-y) --> y - x where x <= y)
       if (IntMinIsPoison)
         return BinaryOperator::CreateNSWNeg(IIOperand);
       return BinaryOperator::CreateNeg(IIOperand);


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