[InstCombine] Fold abs of known negative operand when source is sub

When abs source comes from (x - y), check if a "x > y" dominating
condition exists.

Fixes #54132

Differential Revision: https://reviews.llvm.org/D122013

Author: bcl5980

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -812,6 +812,10 @@ static Optional<bool> getKnownSign(Value *Op, Instruction *CxtI,
   if (Known.isNegative())
     return true;
 
+  Value *X, *Y;
+  if (match(Op, m_NSWSub(m_Value(X), m_Value(Y))))
+    return isImpliedByDomCondition(ICmpInst::ICMP_SLT, X, Y, CxtI, DL);
+
   return isImpliedByDomCondition(
       ICmpInst::ICMP_SLT, Op, Constant::getNullValue(Op->getType()), CxtI, DL);
 }

llvm/test/Transforms/InstCombine/abs-intrinsic.ll

@@ -433,10 +433,9 @@ define i32 @sub_abs_gt(i32 %x, i32 %y) {
 ; CHECK-NEXT:    br i1 [[CMP]], label [[COND_TRUE:%.*]], label [[COND_END:%.*]]
 ; 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:    br label [[COND_END]]
 ; CHECK:       cond.end:
-; CHECK-NEXT:    [[R:%.*]] = phi i32 [ [[TMP0]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[R:%.*]] = phi i32 [ [[SUB]], [[COND_TRUE]] ], [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
 entry:
@@ -456,14 +455,13 @@ cond.end:
 define i32 @sub_abs_lt(i32 %x, i32 %y) {
 ; CHECK-LABEL: @sub_abs_lt(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[Y:%.*]], [[X:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[COND_TRUE:%.*]], label [[COND_END:%.*]]
 ; 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:
@@ -483,14 +481,13 @@ cond.end:
 define i32 @sub_abs_lt_min_not_poison(i32 %x, i32 %y) {
 ; CHECK-LABEL: @sub_abs_lt_min_not_poison(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[Y:%.*]], [[X:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP]], label [[COND_TRUE:%.*]], label [[COND_END:%.*]]
 ; CHECK:       cond.true:
-; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i32 [[X]], [[Y]]
-; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.abs.i32(i32 [[SUB]], i1 false)
+; 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: