[InstCombine] Canonicalize sadd.with.overflow with clamp to sadd.sat

This adds to D69245, adding extra signed patterns for folding from a
sadd_with_overflow to a sadd_sat. These are more complex than the
unsigned patterns, as the overflow can occur in either direction.

For the add case, the positive overflow can only occur if both of the
values are positive (same for both the values being negative). So there
is an extra select on whether to use the positive or negative overflow
limit.

Differential Revision: https://reviews.llvm.org/D69252

1 files changed, 58 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 8446183cfa1..104835bdfd8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1734,6 +1734,8 @@ static Instruction *foldAddSubSelect(SelectInst &SI,
 
 /// Turn X + Y overflows ? -1 : X + Y -> uadd_sat X, Y
 /// And X - Y overflows ? 0 : X - Y -> usub_sat X, Y
+/// Along with a number of patterns similar to:
+/// X + Y overflows ? (X < 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
 static Instruction *
 foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
   Value *CondVal = SI.getCondition();
@@ -1745,6 +1747,50 @@ foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
       !match(FalseVal, m_ExtractValue<0>(m_Specific(II))))
     return nullptr;
 
+  Value *X = II->getLHS();
+  Value *Y = II->getRHS();
+
+  auto IsSignedSaturateLimit = [&](Value *Limit) {
+    Type *Ty = Limit->getType();
+
+    ICmpInst::Predicate Pred;
+    Value *TrueVal, *FalseVal, *Op;
+    const APInt *C;
+    if (!match(Limit, m_Select(m_ICmp(Pred, m_Value(Op), m_APInt(C)),
+                               m_Value(TrueVal), m_Value(FalseVal))))
+      return false;
+
+    auto IsZeroOrOne = [](const APInt &C) {
+      return C.isNullValue() || C.isOneValue();
+    };
+    auto IsMinMax = [&](Value *Min, Value *Max) {
+      APInt MinVal = APInt::getSignedMinValue(Ty->getScalarSizeInBits());
+      APInt MaxVal = APInt::getSignedMaxValue(Ty->getScalarSizeInBits());
+      return match(Min, m_SpecificInt(MinVal)) &&
+             match(Max, m_SpecificInt(MaxVal));
+    };
+
+    if (Op != X && Op != Y)
+      return false;
+
+    // X + Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (X <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    if (Pred == ICmpInst::ICMP_SLT && IsZeroOrOne(*C) &&
+        IsMinMax(TrueVal, FalseVal))
+      return true;
+    // X + Y overflows ? (X >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    if (Pred == ICmpInst::ICMP_SGT && IsZeroOrOne(*C + 1) &&
+        IsMinMax(FalseVal, TrueVal))
+      return true;
+
+    return false;
+  };
+
   Intrinsic::ID NewIntrinsicID;
   if (II->getIntrinsicID() == Intrinsic::uadd_with_overflow &&
       match(TrueVal, m_AllOnes()))
@@ -1754,12 +1800,23 @@ foldOverflowingAddSubSelect(SelectInst &SI, InstCombiner::BuilderTy &Builder) {
            match(TrueVal, m_Zero()))
     // X - Y overflows ? 0 : X - Y -> usub_sat X, Y
     NewIntrinsicID = Intrinsic::usub_sat;
+  else if (II->getIntrinsicID() == Intrinsic::sadd_with_overflow &&
+           IsSignedSaturateLimit(TrueVal))
+    // X + Y overflows ? (X <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (X <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (X >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (X >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y <s 0 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y <s 1 ? INTMIN : INTMAX) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y >s 0 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    // X + Y overflows ? (Y >s -1 ? INTMAX : INTMIN) : X + Y --> sadd_sat X, Y
+    NewIntrinsicID = Intrinsic::sadd_sat;
   else
     return nullptr;
 
   Function *F =
       Intrinsic::getDeclaration(SI.getModule(), NewIntrinsicID, SI.getType());
-  return CallInst::Create(F, {II->getArgOperand(0), II->getArgOperand(1)});
+  return CallInst::Create(F, {X, Y});
 }
 
 Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {