clang crashes on valid code at -O1 and above: Instruction does not dominate all uses!

[zhendongsu]

Bugzilla Link	51241
Resolution	FIXED
Resolved on	Oct 11, 2021 20:29
Version	trunk
OS	All
Blocks	#51489
CC	@topperc,@LebedevRI,@RKSimon,@rotateright
Fixed by commit(s)	5b83261 2f43c81

Extended Description

It appears to be a recent regression.

[515] % clangtk -v
clang version 14.0.0 (https://github.com/llvm/llvm-project.git 0a1ca2a)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /local/suz-local/opfuzz/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.5.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@MX32
Selected multilib: .;@m64
[516] %
[516] % clangtk -O0 small.c
[517] %
[517] % clangtk -O1 small.c
Instruction does not dominate all uses!
%div = sdiv i32 7, %0
store i32 %div, i32* @​b, align 4, !tbaa !​3
in function main
fatal error: error in backend: Broken function found, compilation aborted!
clang-14: error: clang frontend command failed with exit code 70 (use -v to see invocation)
clang version 14.0.0 (https://github.com/llvm/llvm-project.git 0a1ca2a)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /local/suz-local/opfuzz/bin
clang-14: note: diagnostic msg:

---

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang-14: note: diagnostic msg: /tmp/small-52fa75.c
clang-14: note: diagnostic msg: /tmp/small-52fa75.sh
clang-14: note: diagnostic msg:

---

[518] %
[518] % cat small.c
int a, b, c = 1, d;
int main() {
a = c;
int f = d && b % c && 7 % c, g = 7 / c;
c = f;
b = g;
return 0;
}

[rotateright]

This is the likely source of the bug:
https://reviews.llvm.org/rGe38b7e894808ec2a0c976ab01e44364f167508d3

[rotateright]

Reduced test, crashes (invalid IR) with "opt -div-rem-pairs":

define i32 @​#51241 (i1 %b1, i1 %b2, i32 %t0) {
entry:
br i1 %b1, label %land.end, label %land.lhs.true

land.lhs.true:
br i1 %b2, label %land.end, label %land.rhs

land.rhs:
%rem2 = srem i32 7, %t0
br label %land.end

land.end:
%div = sdiv i32 7, %t0
ret i32 %div
}

[rotateright]

Should be fixed with:
https://reviews.llvm.org/rG5b83261c1518

Marking as blocker for release 13.0 since it would be a crashing regression.

[tstellar]

Merged: 2f43c81

[tstellar]

mentioned in issue #51489