[InstCombine] Fold negation of calls to ucmp/scmp by swapping its operands (llvm#98360)

Proofs: https://alive2.llvm.org/ce/z/cp_a36

Author: Poseydon42

llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp

@@ -222,6 +222,11 @@ std::array<Value *, 2> Negator::getSortedOperandsOfBinOp(Instruction *I) {
     }
     break;
   }
+  case Instruction::Call:
+    if (auto *CI = dyn_cast<CmpIntrinsic>(I); CI && CI->hasOneUse())
+      return Builder.CreateIntrinsic(CI->getType(), CI->getIntrinsicID(),
+                                     {CI->getRHS(), CI->getLHS()});
+    break;
   default:
     break; // Other instructions require recursive reasoning.
   }

llvm/test/Transforms/InstCombine/scmp.ll

@@ -1,6 +1,8 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; RUN: opt < %s -passes=instcombine -S | FileCheck %s
 
+declare void @use(i8 %value)
+
 define i1 @scmp_eq_0(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i1 @scmp_eq_0(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
@@ -154,3 +156,30 @@ define i1 @scmp_sle_neg_1(i32 %x, i32 %y) {
   %2 = icmp sle i8 %1, -1
   ret i1 %2
 }
+
+; ========== Fold -scmp(x, y) => scmp(y, x) ==========
+define i8 @scmp_negated(i32 %x, i32 %y) {
+; CHECK-LABEL: define i8 @scmp_negated(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[TMP2:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[Y]], i32 [[X]])
+; CHECK-NEXT:    ret i8 [[TMP2]]
+;
+  %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
+  %2 = sub i8 0, %1
+  ret i8 %2
+}
+
+; Negative test: do not fold if the original scmp result is already used
+define i8 @scmp_negated_multiuse(i32 %x, i32 %y) {
+; CHECK-LABEL: define i8 @scmp_negated_multiuse(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.scmp.i8.i32(i32 [[X]], i32 [[Y]])
+; CHECK-NEXT:    call void @use(i8 [[TMP1]])
+; CHECK-NEXT:    [[TMP2:%.*]] = sub nsw i8 0, [[TMP1]]
+; CHECK-NEXT:    ret i8 [[TMP2]]
+;
+  %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
+  call void @use(i8 %1)
+  %2 = sub i8 0, %1
+  ret i8 %2
+}

llvm/test/Transforms/InstCombine/ucmp.ll

@@ -1,6 +1,8 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
 ; RUN: opt < %s -passes=instcombine -S | FileCheck %s
 
+declare void @use(i8 %value)
+
 define i1 @ucmp_eq_0(i32 %x, i32 %y) {
 ; CHECK-LABEL: define i1 @ucmp_eq_0(
 ; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
@@ -154,3 +156,30 @@ define i1 @ucmp_sle_neg_1(i32 %x, i32 %y) {
   %2 = icmp sle i8 %1, -1
   ret i1 %2
 }
+
+; ========== Fold -ucmp(x, y) => ucmp(y, x) ==========
+define i8 @ucmp_negated(i32 %x, i32 %y) {
+; CHECK-LABEL: define i8 @ucmp_negated(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[TMP2:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[Y]], i32 [[X]])
+; CHECK-NEXT:    ret i8 [[TMP2]]
+;
+  %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
+  %2 = sub i8 0, %1
+  ret i8 %2
+}
+
+; Negative test: do not fold if the original ucmp result is already used
+define i8 @ucmp_negated_multiuse(i32 %x, i32 %y) {
+; CHECK-LABEL: define i8 @ucmp_negated_multiuse(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = call i8 @llvm.ucmp.i8.i32(i32 [[X]], i32 [[Y]])
+; CHECK-NEXT:    call void @use(i8 [[TMP1]])
+; CHECK-NEXT:    [[TMP2:%.*]] = sub nsw i8 0, [[TMP1]]
+; CHECK-NEXT:    ret i8 [[TMP2]]
+;
+  %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
+  call void @use(i8 %1)
+  %2 = sub i8 0, %1
+  ret i8 %2
+}