[vectorizer] Tweak the way we do small loop runtime unrolling in the

loop vectorizer to not do so when runtime pointer checks are needed and
share code with the new (not yet enabled) load/store saturation runtime
unrolling. Also ensure that we only consider the runtime checks when the
loop hasn't already been vectorized. If it has, the runtime check cost
has already been paid.

I've fleshed out a test case to cover the scalar unrolling as well as
the vector unrolling and comment clearly why we are or aren't following
the pattern.

llvm-svn: 200530

1 files changed, 42 insertions, 15 deletions

diff --git a/llvm/test/Transforms/LoopVectorize/X86/unroll-small-loops.ll b/llvm/test/Transforms/LoopVectorize/X86/unroll-small-loops.ll
index 1f0944d24d0..d5024bb1321 100644
--- a/llvm/test/Transforms/LoopVectorize/X86/unroll-small-loops.ll
+++ b/llvm/test/Transforms/LoopVectorize/X86/unroll-small-loops.ll
@@ -1,13 +1,26 @@
-; RUN: opt < %s  -loop-vectorize -mtriple=x86_64-apple-macosx10.8.0 -mcpu=corei7-avx -force-vector-width=4 -force-vector-unroll=0 -dce -S | FileCheck %s
+; RUN: opt < %s  -loop-vectorize -mtriple=x86_64-apple-macosx10.8.0 -mcpu=corei7-avx -force-vector-width=4 -force-vector-unroll=0 -dce -S \
+; RUN:   | FileCheck %s --check-prefix=CHECK-VECTOR
+; RUN: opt < %s  -loop-vectorize -mtriple=x86_64-apple-macosx10.8.0 -mcpu=corei7-avx -force-vector-width=1 -force-vector-unroll=0 -dce -S \
+; RUN:   | FileCheck %s --check-prefix=CHECK-SCALAR
 
 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"
 target triple = "x86_64-apple-macosx10.8.0"
-;CHECK-LABEL: @foo(
-;CHECK: load <4 x i32>
-;CHECK-NOT: load <4 x i32>
-;CHECK: store <4 x i32>
-;CHECK-NOT: store <4 x i32>
-;CHECK: ret
+
+; We don't unroll this loop because it has a small constant trip count.
+;
+; CHECK-VECTOR-LABEL: @foo(
+; CHECK-VECTOR: load <4 x i32>
+; CHECK-VECTOR-NOT: load <4 x i32>
+; CHECK-VECTOR: store <4 x i32>
+; CHECK-VECTOR-NOT: store <4 x i32>
+; CHECK-VECTOR: ret
+;
+; CHECK-SCALAR-LABEL: @foo(
+; CHECK-SCALAR: load i32*
+; CHECK-SCALAR-NOT: load i32*
+; CHECK-SCALAR: store i32
+; CHECK-SCALAR-NOT: store i32
+; CHECK-SCALAR: ret
 define i32 @foo(i32* nocapture %A) nounwind uwtable ssp {
   br label %1
 
@@ -26,10 +39,18 @@ define i32 @foo(i32* nocapture %A) nounwind uwtable ssp {
   ret i32 undef
 }
 
-;CHECK-LABEL: @bar(
-;CHECK: store <4 x i32>
-;CHECK: store <4 x i32>
-;CHECK: ret
+; But this is a good small loop to unroll as we don't know of a bound on its
+; trip count.
+;
+; CHECK-VECTOR-LABEL: @bar(
+; CHECK-VECTOR: store <4 x i32>
+; CHECK-VECTOR: store <4 x i32>
+; CHECK-VECTOR: ret
+;
+; CHECK-SCALAR-LABEL: @bar(
+; CHECK-SCALAR: store i32
+; CHECK-SCALAR: store i32
+; CHECK-SCALAR: ret
 define i32 @bar(i32* nocapture %A, i32 %n) nounwind uwtable ssp {
   %1 = icmp sgt i32 %n, 0
   br i1 %1, label %.lr.ph, label %._crit_edge
@@ -49,10 +70,16 @@ define i32 @bar(i32* nocapture %A, i32 %n) nounwind uwtable ssp {
   ret i32 undef
 }
 
-; Also unroll if we need a runtime check.
-; CHECK-LABEL: runtime_chk
-; CHECK: store <4 x float>
-; CHECK: store <4 x float>
+; Also unroll if we need a runtime check but it was going to be added for
+; vectorization anyways.
+; CHECK-VECTOR-LABEL: @runtime_chk(
+; CHECK-VECTOR: store <4 x float>
+; CHECK-VECTOR: store <4 x float>
+;
+; But not if the unrolling would introduce the runtime check.
+; CHECK-SCALAR-LABEL: @runtime_chk(
+; CHECK-SCALAR: store float
+; CHECK-SCALAR-NOT: store float
 define void @runtime_chk(float* %A, float* %B, float %N) {
 entry:
   br label %for.body