PR14448 - prevent the loop vectorizer from vectorizing the same loop twice.

The LoopVectorizer often runs multiple times on the same function due to inlining.
When this happens the loop vectorizer often vectorizes the same loops multiple times, increasing code size and adding unneeded branches.
With this patch, the vectorizer during vectorization puts metadata on scalar loops and marks them as 'already vectorized' so that it knows to ignore them when it sees them a second time.

PR14448.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176399 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 75 insertions, 0 deletions

diff --git a/test/Transforms/LoopVectorize/vectorize-once.ll b/test/Transforms/LoopVectorize/vectorize-once.ll
new file mode 100644
index 0000000..ac16948
--- /dev/null
+++ b/test/Transforms/LoopVectorize/vectorize-once.ll
@@ -0,0 +1,75 @@
+; RUN: opt < %s -loop-vectorize -force-vector-unroll=1 -force-vector-width=4 -dce -instcombine -S -simplifycfg | 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"
+target triple = "x86_64-apple-macosx10.8.0"
+
+;
+; We want to make sure that we are vectorizeing the scalar loop only once
+; even if the pass manager runs the vectorizer multiple times due to inlining.
+
+
+; This test checks that we add metadata to vectorized loops
+; CHECK: _Z4foo1Pii
+; CHECK: <4 x i32>
+; CHECK: llvm.vectorizer.already_vectorized
+; CHECK: ret
+
+; This test comes from the loop:
+;
+;int foo (int *A, int n) {
+;  return std::accumulate(A, A + n, 0);
+;}
+define i32 @_Z4foo1Pii(i32* %A, i32 %n) #0 {
+entry:
+  %idx.ext = sext i32 %n to i64
+  %add.ptr = getelementptr inbounds i32* %A, i64 %idx.ext
+  %cmp3.i = icmp eq i32 %n, 0
+  br i1 %cmp3.i, label %_ZSt10accumulateIPiiET0_T_S2_S1_.exit, label %for.body.i
+
+for.body.i:                                       ; preds = %entry, %for.body.i
+  %__init.addr.05.i = phi i32 [ %add.i, %for.body.i ], [ 0, %entry ]
+  %__first.addr.04.i = phi i32* [ %incdec.ptr.i, %for.body.i ], [ %A, %entry ]
+  %0 = load i32* %__first.addr.04.i, align 4, !tbaa !0
+  %add.i = add nsw i32 %0, %__init.addr.05.i
+  %incdec.ptr.i = getelementptr inbounds i32* %__first.addr.04.i, i64 1
+  %cmp.i = icmp eq i32* %incdec.ptr.i, %add.ptr
+  br i1 %cmp.i, label %_ZSt10accumulateIPiiET0_T_S2_S1_.exit, label %for.body.i
+
+_ZSt10accumulateIPiiET0_T_S2_S1_.exit:            ; preds = %for.body.i, %entry
+  %__init.addr.0.lcssa.i = phi i32 [ 0, %entry ], [ %add.i, %for.body.i ]
+  ret i32 %__init.addr.0.lcssa.i
+}
+
+; This test checks that we don't vectorize loops that are marked with the "already vectorized" metadata.
+; CHECK: _Z4foo2Pii
+; CHECK-NOT: <4 x i32>
+; CHECK: llvm.vectorizer.already_vectorized
+; CHECK: ret
+define i32 @_Z4foo2Pii(i32* %A, i32 %n) #0 {
+entry:
+  %idx.ext = sext i32 %n to i64
+  %add.ptr = getelementptr inbounds i32* %A, i64 %idx.ext
+  %cmp3.i = icmp eq i32 %n, 0
+  br i1 %cmp3.i, label %_ZSt10accumulateIPiiET0_T_S2_S1_.exit, label %for.body.i
+
+for.body.i:                                       ; preds = %entry, %for.body.i
+  %__init.addr.05.i = phi i32 [ %add.i, %for.body.i ], [ 0, %entry ]
+  %__first.addr.04.i = phi i32* [ %incdec.ptr.i, %for.body.i ], [ %A, %entry ]
+  %0 = load i32* %__first.addr.04.i, align 4, !tbaa !0
+  %add.i = add nsw i32 %0, %__init.addr.05.i
+  %incdec.ptr.i = getelementptr inbounds i32* %__first.addr.04.i, i64 1
+  %cmp.i = icmp eq i32* %incdec.ptr.i, %add.ptr
+  br i1 %cmp.i, label %_ZSt10accumulateIPiiET0_T_S2_S1_.exit, label %for.body.i, !llvm.vectorizer.already_vectorized !3
+
+_ZSt10accumulateIPiiET0_T_S2_S1_.exit:            ; preds = %for.body.i, %entry
+  %__init.addr.0.lcssa.i = phi i32 [ 0, %entry ], [ %add.i, %for.body.i ]
+  ret i32 %__init.addr.0.lcssa.i
+}
+
+attributes #0 = { nounwind readonly ssp uwtable "fp-contract-model"="standard" "no-frame-pointer-elim" "no-frame-pointer-elim-non-leaf" "realign-stack" "relocation-model"="pic" "ssp-buffers-size"="8" }
+
+!0 = metadata !{metadata !"int", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA"}
+!3 = metadata !{}
+