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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185299 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 39 insertions, 0 deletions

diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index f41bd28776..e6e0f6b6ae 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/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) {
diff --git a/test/Transforms/LoopVectorize/funcall.ll b/test/Transforms/LoopVectorize/funcall.ll
new file mode 100644
index 0000000000..0fb929f65c
--- /dev/null
+++ b/test/Transforms/LoopVectorize/funcall.ll
@@ -0,0 +1,32 @@
+; RUN: opt -S -loop-vectorize -force-vector-width=2 -force-vector-unroll=1 < %s | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+; Make sure we can vectorize loops with functions to math library functions.
+; They might read the rounding mode but we are only vectorizing loops that
+; contain a limited set of function calls and none of them sets the rounding
+; mode, so vectorizing them is safe.
+
+; CHECK: test
+; CHECK: <2 x double>
+
+define void @test(double* %d, double %t) {
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds double* %d, i64 %indvars.iv
+  %0 = load double* %arrayidx, align 8
+  %1 = tail call double @llvm.pow.f64(double %0, double %t)
+  store double %1, double* %arrayidx, align 8
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
+  %exitcond = icmp ne i32 %lftr.wideiv, 128
+  br i1 %exitcond, label %for.body, label %for.end
+
+for.end:
+  ret void
+}
+
+declare double @llvm.pow.f64(double, double)