[InstCombine] Support folding a subtract with a constant LHS into a phi node

We currently only support folding a subtract into a select but not a PHI. This fixes that.

I had to fix an assumption in FoldOpIntoPhi that assumed the PHI node was always in operand 0. Now we pass it in like we do for FoldOpIntoSelect. But we still require some dancing to find the Constant when we create the BinOp or ConstantExpr. This is based code is similar to what we do for selects.

Since I touched all call sites, this also renames FoldOpIntoPhi to foldOpIntoPhi to match coding standards.

Differential Revision: https://reviews.llvm.org/D31686

llvm-svn: 300363

1 files changed, 3 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index a238f3f0505..f1ac82057e6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1455,16 +1455,16 @@ Instruction *InstCombiner::commonIRemTransforms(BinaryOperator &I) {
       if (SelectInst *SI = dyn_cast<SelectInst>(Op0I)) {
         if (Instruction *R = FoldOpIntoSelect(I, SI))
           return R;
-      } else if (isa<PHINode>(Op0I)) {
+      } else if (auto *PN = dyn_cast<PHINode>(Op0I)) {
         using namespace llvm::PatternMatch;
         const APInt *Op1Int;
         if (match(Op1, m_APInt(Op1Int)) && !Op1Int->isMinValue() &&
             (I.getOpcode() == Instruction::URem ||
              !Op1Int->isMinSignedValue())) {
-          // FoldOpIntoPhi will speculate instructions to the end of the PHI's
+          // foldOpIntoPhi will speculate instructions to the end of the PHI's
           // predecessor blocks, so do this only if we know the srem or urem
           // will not fault.
-          if (Instruction *NV = FoldOpIntoPhi(I))
+          if (Instruction *NV = foldOpIntoPhi(I, PN))
             return NV;
         }
       }