LoopVectorize: Math functions only read rounding mode

Math functions are mark as readonly because they read the floating point
rounding mode. Because we don't vectorize loops that would contain function
calls that set the rounding mode it is safe to ignore this memory read.

llvm-svn: 185299

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
index f41bd28776b..e6e0f6b6ae4 100644
--- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -3520,6 +3520,13 @@ bool LoopVectorizationLegality::canVectorizeMemory() {
       // but is not a load, then we quit. Notice that we don't handle function
       // calls that read or write.
       if (it->mayReadFromMemory()) {
+        // Many math library functions read the rounding mode. We will only
+        // vectorize a loop if it contains known function calls that don't set
+        // the flag. Therefore, it is safe to ignore this read from memory.
+        CallInst *Call = dyn_cast<CallInst>(it);
+        if (Call && getIntrinsicIDForCall(Call, TLI))
+          continue;
+
         LoadInst *Ld = dyn_cast<LoadInst>(it);
         if (!Ld) return false;
         if (!Ld->isSimple() && !IsAnnotatedParallel) {