vitalybuka added subscribers: eugenis, guiand, vitalybuka.
vitalybuka added a comment.
After this patch we have false msan reports on code like this:
bool iv_compare2(const int *op1, const int *op2) {
if (op1[1] != op2[1]) return op1[1] < op2[1];
for (int i = 1; i >= 0; i--) {
if (op1[i] != op2[i]) return op1[i] < op2[i];
}
return false;
}
void foo() {
int a[2] = {};
int b[2] = {};
auto UNINITIALIZED= iv_compare2(a, b);
}
Here it looks fine and the same as before the patch. It returns "and undef,
false" which should be false.
*** IR Dump After Simplify the CFG ***
; Function Attrs: norecurse nounwind readonly sanitize_memory uwtable
define zeroext i1 @_Z11iv_compare2PKiS0_(i32* nocapture readonly %op1, i32*
nocapture readonly %op2) local_unnamed_addr #0 !dbg !8 {
entry:
%arrayidx = getelementptr inbounds i32, i32* %op1, i64 1, !dbg !10
%0 = load i32, i32* %arrayidx, align 4, !dbg !10
%arrayidx1 = getelementptr inbounds i32, i32* %op2, i64 1, !dbg !11
%1 = load i32, i32* %arrayidx1, align 4, !dbg !11
%cmp.not = icmp eq i32 %0, %1, !dbg !12
br i1 %cmp.not, label %for.cond, label %if.then, !dbg !10
if.then: ; preds = %entry
%cmp4 = icmp slt i32 %0, %1, !dbg !13
ret i1 %cmp4, !dbg !14
for.cond: ; preds = %entry
%2 = load i32, i32* %op1, align 4, !dbg !15
%3 = load i32, i32* %op2, align 4, !dbg !16
%cmp9.not.1 = icmp eq i32 %2, %3, !dbg !17
%cmp15 = icmp slt i32 %2, %3
%spec.select39 = select i1 %cmp9.not.1, i1 undef, i1 %cmp15, !dbg !15
%spec.select40 = select i1 %cmp9.not.1, i1 false, i1 true, !dbg !15
%spec.select = and i1 %spec.select39, %spec.select40
ret i1 %spec.select
}
However with this patch after the next transformation it breaks the code:
Now it returns undef instead of false if %2 == %3
*** IR Dump After Combine redundant instructions ***
; Function Attrs: norecurse nounwind readonly sanitize_memory uwtable
define zeroext i1 @_Z11iv_compare2PKiS0_(i32* nocapture readonly %op1, i32*
nocapture readonly %op2) local_unnamed_addr #0 !dbg !8 {
entry:
%arrayidx = getelementptr inbounds i32, i32* %op1, i64 1, !dbg !10
%0 = load i32, i32* %arrayidx, align 4, !dbg !10
%arrayidx1 = getelementptr inbounds i32, i32* %op2, i64 1, !dbg !11
%1 = load i32, i32* %arrayidx1, align 4, !dbg !11
%cmp.not = icmp eq i32 %0, %1, !dbg !12
br i1 %cmp.not, label %for.cond, label %if.then, !dbg !10
if.then: ; preds = %entry
%cmp4 = icmp slt i32 %0, %1, !dbg !13
ret i1 %cmp4, !dbg !14
for.cond: ; preds = %entry
%2 = load i32, i32* %op1, align 4, !dbg !15
%3 = load i32, i32* %op2, align 4, !dbg !16
%cmp9.not.1 = icmp eq i32 %2, %3, !dbg !17
%cmp15 = icmp slt i32 %2, %3
%spec.select39 = select i1 %cmp9.not.1, i1 undef, i1 %cmp15, !dbg !15
ret i1 %spec.select39
}
The msan reasonably reports a bug.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D83360/new/
https://reviews.llvm.org/D83360
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