[PATCH] D141188: [MergeICmps] Adapt to non-eq comparisons

[Arthur Eubanks via Phabricator via llvm-commits]

aeubanks added a comment.

miscompile:

  $ cat a.ll
  target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"                                                                                                       
  target triple = "x86_64-unknown-linux-gnu"                                                                                                                                                         
                                                                                                                                                                                                     
  %"struct.media::WebrtcVideoStatsDB::VideoDescKey" = type { i8, i32, i8, i32 }                                                                                                                      
                                                                                                                                                                                                     
  define i1 @_ZN5medianeERKNS_18WebrtcVideoStatsDB12VideoDescKeyES3_(ptr nocapture noundef readonly align 4 dereferenceable(16) %0, ptr nocapture noundef readonly align 4 dereferenceable(16) %1) { 
    %3 = load i8, ptr %0, align 4, !range !4, !noundef !5
    %4 = load i8, ptr %1, align 4, !range !4, !noundef !5
    %5 = icmp eq i8 %3, %4
    br i1 %5, label %6, label %24
  
  6:                                                ; preds = %2
    %7 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %0, i64 0, i32 1
    %8 = load i32, ptr %7, align 4
    %9 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %1, i64 0, i32 1
    %10 = load i32, ptr %9, align 4
    %11 = icmp eq i32 %8, %10
    br i1 %11, label %12, label %24
  
  12:                                               ; preds = %6
    %13 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %0, i64 0, i32 2
    %14 = load i8, ptr %13, align 4, !range !4, !noundef !5
    %15 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %1, i64 0, i32 2
    %16 = load i8, ptr %15, align 4, !range !4, !noundef !5
    %17 = icmp eq i8 %14, %16
    br i1 %17, label %18, label %24
  
  18:                                               ; preds = %12
    %19 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %0, i64 0, i32 3
    %20 = load i32, ptr %19, align 4
    %21 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %1, i64 0, i32 3
    %22 = load i32, ptr %21, align 4
    %23 = icmp ne i32 %20, %22
    br label %24
  
  24:                                               ; preds = %18, %12, %6, %2
    %25 = phi i1 [ true, %12 ], [ true, %6 ], [ true, %2 ], [ %23, %18 ]
    ret i1 %25
  }
  
  !4 = !{i8 0, i8 2}
  !5 = !{}
  $ opt -passes=mergeicmps -S a.ll
  target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
  target triple = "x86_64-unknown-linux-gnu"
  
  %"struct.media::WebrtcVideoStatsDB::VideoDescKey" = type { i8, i32, i8, i32 }
  
  define i1 @_ZN5medianeERKNS_18WebrtcVideoStatsDB12VideoDescKeyES3_(ptr nocapture noundef readonly align 4 dereferenceable(16) %0, ptr nocapture noundef readonly align 4 dereferenceable(16) %1) {
    %3 = load i8, ptr %0, align 1
    %4 = load i8, ptr %1, align 1
    %5 = icmp eq i8 %3, %4
    br i1 %5, label %6, label %16
  
  6:                                                ; preds = %2
    %7 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %0, i64 0, i32 1
    %8 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %1, i64 0, i32 1
    %memcmp = call i32 @memcmp(ptr %7, ptr %8, i64 5)
    %9 = icmp eq i32 %memcmp, 0
    br i1 %9, label %10, label %16
  
  10:                                               ; preds = %6
    %11 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %0, i64 0, i32 3
    %12 = getelementptr inbounds %"struct.media::WebrtcVideoStatsDB::VideoDescKey", ptr %1, i64 0, i32 3
    %13 = load i32, ptr %11, align 4
    %14 = load i32, ptr %12, align 4
    %15 = icmp ne i32 %13, %14
    br label %16
  
  16:                                               ; preds = %2, %6, %10
    %17 = phi i1 [ %15, %10 ], [ false, %6 ], [ false, %2 ]
    ret i1 %17
  }
  
  ; Function Attrs: nofree nounwind willreturn memory(argmem: read)
  declare i32 @memcmp(ptr nocapture, ptr nocapture, i64) #0
  
  attributes #0 = { nofree nounwind willreturn memory(argmem: read) }

the phi value from the entry block turns from `true` to `false`
(also the metadata for the loads in the entry block don't need to be dropped?)

will revert this patch


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D141188/new/

https://reviews.llvm.org/D141188