When InstCombine tries to fold away (fsub x, (fneg y)) into (fadd x, y), it is

also worthwhile for it to look through FP extensions and truncations, whose
application commutes with fneg.

llvm-svn: 187249

1 files changed, 13 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0aa301bc7a8..8d4677b0ec6 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1528,9 +1528,21 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
       if (Instruction *NV = FoldOpIntoSelect(I, SI))
         return NV;
 
-  // If this is a 'B = x-(-A)', change to B = x+A...
+  // If this is a 'B = x-(-A)', change to B = x+A, potentially looking
+  // through FP extensions/truncations along the way.
   if (Value *V = dyn_castFNegVal(Op1))
     return BinaryOperator::CreateFAdd(Op0, V);
+  if (FPTruncInst *FPTI = dyn_cast<FPTruncInst>(Op1)) {
+    if (Value *V = dyn_castFNegVal(FPTI->getOperand(0))) {
+      Value *NewTrunc = Builder->CreateFPTrunc(V, I.getType());
+      return BinaryOperator::CreateFAdd(Op0, NewTrunc);
+    }
+  } else if (FPExtInst *FPEI = dyn_cast<FPExtInst>(Op1)) {
+    if (Value *V = dyn_castFNegVal(FPEI->getOperand(0))) {
+      Value *NewTrunc = Builder->CreateFPExt(V, I.getType());
+      return BinaryOperator::CreateFAdd(Op0, NewTrunc);
+    }
+  }
 
   if (I.hasUnsafeAlgebra()) {
     if (Value *V = FAddCombine(Builder).simplify(&I))