[InstSimplify] Add SimplifyFPBinOp function.

It is a variation of SimplifyBinOp, but it takes into account
FastMathFlags.

It is needed in inliner and loop-unroller to accurately predict the
transformation's outcome (previously we dropped the flags and were too
conservative in some cases).

Example:
float foo(float *a, float b) {
 float r;
 if (a[1] * b)
   r = /* a lot of expensive computations */;
 else
   r = 1;
 return r;
}
float boo(float *a) {
 return foo(a, 0.0);
}

Without this patch, we don't inline 'foo' into 'boo'.

llvm-svn: 228432

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
index bd9da14f669..87237c62299 100644
--- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp
@@ -311,7 +311,12 @@ class UnrollAnalyzer : public InstVisitor<UnrollAnalyzer, bool> {
     if (!isa<Constant>(RHS))
       if (Constant *SimpleRHS = SimplifiedValues.lookup(RHS))
         RHS = SimpleRHS;
-    Value *SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS);
+    Value *SimpleV = nullptr;
+    if (auto FI = dyn_cast<FPMathOperator>(&I))
+      SimpleV =
+          SimplifyFPBinOp(I.getOpcode(), LHS, RHS, FI->getFastMathFlags());
+    else
+      SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS);
 
     if (SimpleV && CountedInsns.insert(&I).second)
       NumberOfOptimizedInstructions += TTI.getUserCost(&I);