[PATCH] D69245: [InstCombine] Canonicalize uadd.with.overflow to uadd.sat

[Dave Green via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGa5f7bc0de72f: [InstCombine] Canonicalize uadd.with.overflow to uadd.sat (authored by dmgreen).

Changed prior to commit:
  https://reviews.llvm.org/D69245?vs=226861&id=227274#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D69245/new/

https://reviews.llvm.org/D69245

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/overflow_to_sat.ll


Index: llvm/test/Transforms/InstCombine/overflow_to_sat.ll
===================================================================
--- llvm/test/Transforms/InstCombine/overflow_to_sat.ll
+++ llvm/test/Transforms/InstCombine/overflow_to_sat.ll
@@ -3,10 +3,7 @@
 
 define i32 @uadd(i32 %x, i32 %y) {
 ; CHECK-LABEL: @uadd(
-; CHECK-NEXT:    [[AO:%.*]] = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
-; CHECK-NEXT:    [[O:%.*]] = extractvalue { i32, i1 } [[AO]], 1
-; CHECK-NEXT:    [[A:%.*]] = extractvalue { i32, i1 } [[AO]], 0
-; CHECK-NEXT:    [[S:%.*]] = select i1 [[O]], i32 -1, i32 [[A]]
+; CHECK-NEXT:    [[S:%.*]] = call i32 @llvm.uadd.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
 ; CHECK-NEXT:    ret i32 [[S]]
 ;
   %ao = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 %x, i32 %y)
@@ -18,10 +15,7 @@
 
 define i32 @usub(i32 %x, i32 %y) {
 ; CHECK-LABEL: @usub(
-; CHECK-NEXT:    [[AO:%.*]] = tail call { i32, i1 } @llvm.usub.with.overflow.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
-; CHECK-NEXT:    [[O:%.*]] = extractvalue { i32, i1 } [[AO]], 1
-; CHECK-NEXT:    [[A:%.*]] = extractvalue { i32, i1 } [[AO]], 0
-; CHECK-NEXT:    [[S:%.*]] = select i1 [[O]], i32 0, i32 [[A]]
+; CHECK-NEXT:    [[S:%.*]] = call i32 @llvm.usub.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])
 ; CHECK-NEXT:    ret i32 [[S]]
 ;
   %ao = tail call { i32, i1 } @llvm.usub.with.overflow.i32(i32 %x, i32 %y)
Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1732,6 +1732,36 @@
   return nullptr;
 }
 
+/// Turn X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
+/// And X - Y overflows ? 0 : X - Y -> usub_sat X, Y
+static Instruction *
+foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
+  Value *CondVal = SI.getCondition();
+  Value *TrueVal = SI.getTrueValue();
+  Value *FalseVal = SI.getFalseValue();
+
+  WithOverflowInst *II;
+  if (!match(CondVal, m_ExtractValue<1>(m_WithOverflowInst(II))) ||
+      !match(FalseVal, m_ExtractValue<0>(m_Specific(II))))
+    return nullptr;
+
+  Intrinsic::ID NewIntrinsicID;
+  if (II->getIntrinsicID() == Intrinsic::uadd_with_overflow &&
+      match(TrueVal, m_AllOnes()))
+    // X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
+    NewIntrinsicID = Intrinsic::uadd_sat;
+  else if (II->getIntrinsicID() == Intrinsic::usub_with_overflow &&
+           match(TrueVal, m_Zero()))
+    // X - Y overflows ? 0 : X - Y -> usub_sat X, Y
+    NewIntrinsicID = Intrinsic::usub_sat;
+  else
+    return nullptr;
+
+  Function *F =
+      Intrinsic::getDeclaration(SI.getModule(), NewIntrinsicID, SI.getType());
+  return CallInst::Create(F, {II->getArgOperand(0), II->getArgOperand(1)});
+}
+
 Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {
   Constant *C;
   if (!match(Sel.getTrueValue(), m_Constant(C)) &&
@@ -2398,6 +2428,8 @@
 
   if (Instruction *Add = foldAddSubSelect(SI, Builder))
     return Add;
+  if (Instruction *Add = foldOverflowingAddSubSelect(SI, Builder))
+    return Add;
 
   // Turn (select C, (op X, Y), (op X, Z)) -> (op X, (select C, Y, Z))
   auto *TI = dyn_cast<Instruction>(TrueVal);


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