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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187249 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 25 insertions, 1 deletions

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0aa301bc7a..8d4677b0ec 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/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))
diff --git a/test/Transforms/InstCombine/fneg-ext.ll b/test/Transforms/InstCombine/fneg-ext.ll
new file mode 100644
index 0000000000..49ad232526
--- /dev/null
+++ b/test/Transforms/InstCombine/fneg-ext.ll
@@ -0,0 +1,12 @@
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+; CHECK: test1
+define double @test1(float %a, double %b) nounwind readnone ssp uwtable {
+; CHECK-NOT: fsub
+; CHECK: fpext
+; CHECK: fadd
+  %1 = fsub float -0.000000e+00, %a
+  %2 = fpext float %1 to double
+  %3 = fsub double %b, %2
+  ret double %3
+}