[polly] r219131 - [Fix] Dead statements should not confuse the RTC generation

[Tobias Grosser]

On 07/10/2014 17:16, Johannes Doerfert wrote:
> I don't know why this happens but the assertion is not crucial, thus we
> could just apply the attached patch.
>
> Thoughts?

The patch seems to ignore alias groups with one element. As far as I 
understand those should not have been computed in the first place. I 
would prefer to understand why they are computed and avoid computing 
them, if possible. I reduced you a test case. Maybe this helps to 
understand the bug:

polly-opt  -basicaa -polly-scops -polly-code-generator=isl out4.ll -analyze

opt: 
/home/grosser/Projects/polly/git/tools/polly/lib/Analysis/ScopInfo.cpp:1300: 
bool polly::Scop::buildAliasGroups(llvm::AliasAnalysis &): Assertion 
`AG.size() > 1 && "Alias groups should contain at least two accesses"' 
failed.

Cheers,
Tobias
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

@dct_luma_16x16.M4 = external global [4 x [4 x i32]], align 16
@dct_luma_16x16.M5 = external global [4 x i32], align 16
@dct_luma_16x16.M0 = external global [4 x [4 x [4 x [4 x i32]]]], align 16

define void @dct_luma_16x16() {
.preheader29.preheader:                           ; preds = %.split
  br label %.preheader29

.preheader29:                                     ; preds = %bb12, %.preheader29.preheader
  %indvar253 = phi i64 [ %tmp13, %bb12 ], [ 0, %.preheader29.preheader ]
  br label %.preheader28

.preheader28:                                     ; preds = %bb10, %.preheader29
  %indvar255 = phi i64 [ 0, %.preheader29 ], [ %tmp11, %bb10 ]
  br label %bb6

bb6:                                              ; preds = %bb6, %.preheader28
  %indvar250 = phi i64 [ 0, %.preheader28 ], [ %tmp, %bb6 ]
  %scevgep263 = getelementptr [4 x [4 x i32]]* @dct_luma_16x16.M4, i64 0, i64 %indvar250, i64 1
  store i32 undef, i32* %scevgep263, align 4
  %tmp = add i64 %indvar250, 1
  %exitcond126 = icmp eq i64 %tmp, 4
  br i1 %exitcond126, label %.preheader27.preheader, label %bb6

.preheader27.preheader:                           ; preds = %bb6
  br label %.preheader27

.preheader27:                                     ; preds = %.preheader27, %.preheader27.preheader
  %indvar265 = phi i64 [ %tmp9, %.preheader27 ], [ 0, %.preheader27.preheader ]
  %scevgep268 = getelementptr [4 x [4 x i32]]* @dct_luma_16x16.M4, i64 0, i64 0, i64 %indvar265
  %tmp7 = load i32* %scevgep268, align 4
  %tmp8 = add nsw i32 undef, %tmp7
  store i32 %tmp8, i32* getelementptr inbounds ([4 x i32]* @dct_luma_16x16.M5, i64 0, i64 0), align 16
  %tmp9 = add i64 %indvar265, 1
  %exitcond135 = icmp eq i64 %tmp9, 4
  br i1 %exitcond135, label %bb10, label %.preheader27

bb10:                                             ; preds = %.preheader27
  %tmp11 = add i64 %indvar255, 1
  %exitcond144 = icmp eq i64 %tmp11, 4
  br i1 %exitcond144, label %bb12, label %.preheader28

bb12:                                             ; preds = %bb10
  %tmp13 = add i64 %indvar253, 1
  %exitcond159 = icmp eq i64 %tmp13, 4
  br i1 %exitcond159, label %.preheader25.preheader, label %.preheader29

.preheader25.preheader:                           ; preds = %bb12
  br label %.preheader25

.preheader25:                                     ; preds = %bb16, %.preheader25.preheader
  %indvar243 = phi i64 [ %tmp17, %bb16 ], [ 0, %.preheader25.preheader ]
  br label %bb14

bb14:                                             ; preds = %bb14, %.preheader25
  %indvar240 = phi i64 [ 0, %.preheader25 ], [ %tmp15, %bb14 ]
  %scevgep246 = getelementptr [4 x [4 x i32]]* @dct_luma_16x16.M4, i64 0, i64 %indvar243, i64 %indvar240
  store i32 undef, i32* %scevgep246, align 4
  %tmp15 = add i64 %indvar240, 1
  %exitcond120 = icmp eq i64 %tmp15, 4
  br i1 %exitcond120, label %bb16, label %bb14

bb16:                                             ; preds = %bb14
  %tmp17 = add i64 %indvar243, 1
  %exitcond123 = icmp eq i64 %tmp17, 4
  br i1 %exitcond123, label %.preheader24.preheader, label %.preheader25

.preheader24.preheader:                           ; preds = %bb16
  br label %.preheader24

.preheader24:                                     ; preds = %.preheader24, %.preheader24.preheader
  %indvar233 = phi i64 [ %tmp18, %.preheader24 ], [ 0, %.preheader24.preheader ]
  %scevgep238 = getelementptr [4 x [4 x i32]]* @dct_luma_16x16.M4, i64 0, i64 %indvar233, i64 1
  store i32 undef, i32* %scevgep238, align 4
  %tmp18 = add i64 %indvar233, 1
  %exitcond115 = icmp eq i64 %tmp18, 4
  br i1 %exitcond115, label %.preheader23.preheader, label %.preheader24

.preheader23.preheader:                           ; preds = %.preheader24
  br label %.preheader23

.preheader23:                                     ; preds = %.preheader23, %.preheader23.preheader
  %indvar226 = phi i64 [ %tmp19, %.preheader23 ], [ 0, %.preheader23.preheader ]
  %scevgep232 = getelementptr [4 x [4 x i32]]* @dct_luma_16x16.M4, i64 0, i64 2, i64 %indvar226
  store i32 undef, i32* %scevgep232, align 4
  %tmp19 = add i64 %indvar226, 1
  %exitcond108 = icmp eq i64 %tmp19, 4
  br i1 %exitcond108, label %.preheader22.preheader, label %.preheader23

.preheader22.preheader:                           ; preds = %.preheader23
  br label %.preheader22

.preheader22:                                     ; preds = %bb24, %.preheader22.preheader
  ret void
}