Provide InstCombines for the following 3 cases:

A * (1 - (uitofp i1 C)) -> select C, 0, A
B * (uitofp i1 C) -> select C, B, 0
select C, 0, A + select C, B, 0 -> select C, B, A

These come up in code that has been hand-optimized from a select to a linear blend, 
on platforms where that may have mattered. We want to undo such changes 
with the following transform:
A*(1 - uitofp i1 C) + B*(uitofp i1 C) -> select C, A, B

llvm-svn: 181216

1 files changed, 28 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index df7390652f1..0ac0ca27acf 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -524,6 +524,34 @@ Instruction *InstCombiner::visitFMul(BinaryOperator &I) {
       }
     }
 
+    // B * (uitofp i1 C) -> select C, B, 0
+    if(I.hasNoNaNs() && I.hasNoInfs() && I.hasNoSignedZeros()) {
+        Value *LHS=Op0, *RHS=Op1;
+        Value *B, *C;
+        if (!match(RHS, m_UIToFp(m_Value(C))))
+            std::swap(LHS, RHS);
+
+        if (match(RHS, m_UIToFp(m_Value(C)))) {
+            B=LHS;
+            Value *Zero = ConstantFP::getNegativeZero(B->getType());
+            return SelectInst::Create(C, B, Zero);
+        }
+    }
+
+    // A * (1 - uitofp i1 C) -> select C, 0, A
+    if(I.hasNoNaNs() && I.hasNoInfs() && I.hasNoSignedZeros()) { 
+        Value *LHS=Op0, *RHS=Op1;
+        Value *A, *C;
+        if (!match(RHS, m_FSub(m_FPOne(), m_UIToFp(m_Value(C)))))
+            std::swap(LHS, RHS);
+
+        if (match(RHS, m_FSub(m_FPOne(), m_UIToFp(m_Value(C))))) {
+            A=LHS;
+            Value *Zero = ConstantFP::getNegativeZero(A->getType());
+            return SelectInst::Create(C, Zero, A);
+        }
+    }
+
     if (!isa<Constant>(Op1))
       std::swap(Opnd0, Opnd1);
     else