[LoopVectorize] Change comment for isOutOfScope in collectLoopUniforms, NFC

Update comment for isOutOfScope and add a testcase for uniform value being used
out of scope.

Differential Revision: https://reviews.llvm.org/D23073

llvm-svn: 277515

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -4946,10 +4946,11 @@ void LoopVectorizationLegality::collectLoopScalars() {
 
 void LoopVectorizationLegality::collectLoopUniforms() {
   // We now know that the loop is vectorizable!
-  // Collect variables that will remain uniform after vectorization.
+  // Collect instructions inside the loop that will remain uniform after
+  // vectorization.
 
-  // If V is not an instruction inside the current loop, it is a Value
+  // Global values, params and instructions outside of current loop are out of
-  // outside of the scope which we are interesting in.
+  // scope.
   auto isOutOfScope = [&](Value *V) -> bool {
     Instruction *I = dyn_cast<Instruction>(V);
     return (!I || !TheLoop->contains(I));

llvm/test/Transforms/LoopVectorize/X86/uniform-phi.ll

@@ -48,3 +48,30 @@ for.body:
 for.end:
   ret void
 }
+
+; CHECK-LABEL: goo
+; Check %indvars.iv and %indvars.iv.next are uniform instructions even if they are used outside of loop.
+; CHECK-DAG: LV: Found uniform instruction:   %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+; CHECK-DAG: LV: Found uniform instruction:   %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+; CHECK-DAG: LV: Found uniform instruction:   %exitcond = icmp eq i64 %indvars.iv, 1599
+
+define i64 @goo(float* noalias nocapture %a, float* noalias nocapture readonly %b) #0 {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds float, float* %b, i64 %indvars.iv
+  %tmp0 = load float, float* %arrayidx, align 4
+  %add = fadd float %tmp0, 1.000000e+00
+  %arrayidx5 = getelementptr inbounds float, float* %a, i64 %indvars.iv
+  store float %add, float* %arrayidx5, align 4
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  %exitcond = icmp eq i64 %indvars.iv, 1599
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+  %retval = add i64 %indvars.iv, %indvars.iv.next
+  ret i64 %retval
+}
+