https://llvm.org/bugs/show_bug.cgi?id=27575
Bug ID: 27575
Summary: miscompile of select at O1
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: k...@google.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
#include <stdio.h>
int main(int argc, char **argv) {
int i = argc - 1;
int a = 1 << i;
int b = a >> 1;
double c = b > 0 ? (double)b : 0.5;
printf("%d %g\n", b, c);
}
for f in 0 1 2; do clang++ -O$f bug.cc && ./a.out ; done
0 0.5
0 0
0 0
This is what I see in IR:
*** IR Dump After Dead Argument Elimination ***; ModuleID = 'bug.cc'
%cond = select i1 %cmp, double %conv, double 5.000000e-01
*** IR Dump After Combine redundant instructions ***
%1 = select i1 %0, i32 %shr, i32 0
I don't see how this transformation could be legal.
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