[llvm] [ConstraintElimination] Add support for UCMP/SCMP intrinsics (PR #97974)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (Poseydon42)

<details>
<summary>Changes</summary>

This adds checks to fold calls to `ucmp`/`scmp` where a comparative relationship between the arguments can be established.

---
Full diff: https://github.com/llvm/llvm-project/pull/97974.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Scalar/ConstraintElimination.cpp (+34) 
- (added) llvm/test/Transforms/ConstraintElimination/uscmp.ll (+110) 


``````````diff
diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index bf0c67d9dbc4f..478aea7287875 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -1073,6 +1073,8 @@ void State::addInfoFor(BasicBlock &BB) {
     }
     // Enqueue ssub_with_overflow for simplification.
     case Intrinsic::ssub_with_overflow:
+    case Intrinsic::ucmp:
+    case Intrinsic::scmp:
       WorkList.push_back(
           FactOrCheck::getCheck(DT.getNode(&BB), cast<CallInst>(&I)));
       break;
@@ -1434,6 +1436,33 @@ static bool checkAndReplaceMinMax(MinMaxIntrinsic *MinMax, ConstraintInfo &Info,
   return false;
 }
 
+static bool checkAndReplaceCmp(IntrinsicInst *II, ConstraintInfo &Info,
+                               SmallVectorImpl<Instruction *> &ToRemove) {
+  bool IsSigned = II->getIntrinsicID() == Intrinsic::scmp;
+  Value *LHS = II->getOperand(0);
+  Value *RHS = II->getOperand(1);
+  if (checkCondition(IsSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT, LHS,
+                     RHS, II, Info)
+          .value_or(false)) {
+    II->replaceAllUsesWith(ConstantInt::get(II->getType(), 1));
+    ToRemove.push_back(II);
+    return true;
+  }
+  if (checkCondition(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, LHS,
+                     RHS, II, Info)
+          .value_or(false)) {
+    II->replaceAllUsesWith(ConstantInt::getSigned(II->getType(), -1));
+    ToRemove.push_back(II);
+    return true;
+  }
+  if (checkCondition(ICmpInst::ICMP_EQ, LHS, RHS, II, Info).value_or(false)) {
+    II->replaceAllUsesWith(ConstantInt::get(II->getType(), 0));
+    ToRemove.push_back(II);
+    return true;
+  }
+  return false;
+}
+
 static void
 removeEntryFromStack(const StackEntry &E, ConstraintInfo &Info,
                      Module *ReproducerModule,
@@ -1736,6 +1765,11 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
         Changed |= Simplified;
       } else if (auto *MinMax = dyn_cast<MinMaxIntrinsic>(Inst)) {
         Changed |= checkAndReplaceMinMax(MinMax, Info, ToRemove);
+      } else if (auto *CmpIntrinsic = dyn_cast<IntrinsicInst>(Inst);
+                 CmpIntrinsic &&
+                 (CmpIntrinsic->getIntrinsicID() == Intrinsic::scmp ||
+                  CmpIntrinsic->getIntrinsicID() == Intrinsic::ucmp)) {
+        Changed |= checkAndReplaceCmp(CmpIntrinsic, Info, ToRemove);
       }
       continue;
     }
diff --git a/llvm/test/Transforms/ConstraintElimination/uscmp.ll b/llvm/test/Transforms/ConstraintElimination/uscmp.ll
new file mode 100644
index 0000000000000..16ca93f0427e7
--- /dev/null
+++ b/llvm/test/Transforms/ConstraintElimination/uscmp.ll
@@ -0,0 +1,110 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=constraint-elimination -S %s | FileCheck %s
+
+define i8 @scmp_1(i32 %x, i32 %y) {
+; CHECK-LABEL: @scmp_1(
+; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[TRUE:%.*]], label [[FALSE:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    ret i8 1
+; CHECK:       false:
+; CHECK-NEXT:    ret i8 20
+;
+  %cond = icmp sgt i32 %x, %y
+  br i1 %cond, label %true, label %false
+true:
+  %r = call i8 @llvm.scmp(i32 %x, i32 %y)
+  ret i8 %r
+false:
+  ret i8 20
+}
+
+define i8 @ucmp_1(i32 %x, i32 %y) {
+; CHECK-LABEL: @ucmp_1(
+; CHECK-NEXT:    [[COND:%.*]] = icmp ult i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[TRUE:%.*]], label [[FALSE:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    ret i8 -1
+; CHECK:       false:
+; CHECK-NEXT:    ret i8 20
+;
+  %cond = icmp ult i32 %x, %y
+  br i1 %cond, label %true, label %false
+true:
+  %r = call i8 @llvm.ucmp(i32 %x, i32 %y)
+  ret i8 %r
+false:
+  ret i8 20
+}
+
+define i8 @scmp_2(i32 %x, i32 %y) {
+; CHECK-LABEL: @scmp_2(
+; CHECK-NEXT:    [[COND:%.*]] = icmp sge i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[TRUE:%.*]], label [[FALSE:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    ret i8 20
+; CHECK:       false:
+; CHECK-NEXT:    ret i8 -1
+;
+  %cond = icmp sge i32 %x, %y
+  br i1 %cond, label %true, label %false
+true:
+  ret i8 20
+false:
+  %r = call i8 @llvm.scmp(i32 %x, i32 %y)
+  ret i8 %r
+}
+
+define i8 @ucmp_2(i32 %x, i32 %y) {
+; CHECK-LABEL: @ucmp_2(
+; CHECK-NEXT:    [[COND:%.*]] = icmp ule i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[TRUE:%.*]], label [[FALSE:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    ret i8 20
+; CHECK:       false:
+; CHECK-NEXT:    ret i8 1
+;
+  %cond = icmp ule i32 %x, %y
+  br i1 %cond, label %true, label %false
+true:
+  ret i8 20
+false:
+  %r = call i8 @llvm.ucmp(i32 %x, i32 %y)
+  ret i8 %r
+}
+
+define i8 @scmp_3(i32 %x, i32 %y) {
+; CHECK-LABEL: @scmp_3(
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[TRUE:%.*]], label [[FALSE:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    ret i8 0
+; CHECK:       false:
+; CHECK-NEXT:    ret i8 20
+;
+  %cond = icmp eq i32 %x, %y
+  br i1 %cond, label %true, label %false
+true:
+  %r = call i8 @llvm.scmp(i32 %x, i32 %y)
+  ret i8 %r
+false:
+  ret i8 20
+}
+
+define i8 @ucmp_3(i32 %x, i32 %y) {
+; CHECK-LABEL: @ucmp_3(
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    br i1 [[COND]], label [[TRUE:%.*]], label [[FALSE:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    ret i8 0
+; CHECK:       false:
+; CHECK-NEXT:    ret i8 20
+;
+  %cond = icmp eq i32 %x, %y
+  br i1 %cond, label %true, label %false
+true:
+  %r = call i8 @llvm.ucmp(i32 %x, i32 %y)
+  ret i8 %r
+false:
+  ret i8 20
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/97974