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

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 0aa301bc7a818af11ad1e155c3caa2f41c6776c0..8d4677b0ec62a03e912075473f159a14ef9c49f3 100644 (file)
--- 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 (file)
index 0000000..49ad232
--- /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
+}