[LV] must have a resume value for the canonical IV

[sjoerdmeijer]

Compiling this:

#include <algorithm>
extern char a;
unsigned short e;
long b;
short *c, *d;
void fn1(short f[][3], int g[][3], short h[][3]) {
  for (int i; i < 3ULL; i += 5ULL)
    for (int k; c[i]; k += 2)
#pragma clang loop vectorize_predicate(enable)
      for (int j(((4 ? c[2] : 0) || d[i]) - 1); j < -108 - 18446744073709551485;
           j += 3) {
        a = 0 != f[1][j];
        b = g[1][k] = std::min(e, (unsigned short)h[2][k]);
      }
}

with -Ofast -mcpu=grace -std=c++11 results in:

clang++: llvm-project/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp:9759: void preparePlanForEpilogueVectorLoop(VPlan &, Loop *, const SCEV2ValueTy &, const EpilogueLoopVectorizationInfo &): Assertion `EPResumeVal && "must have a resume value for the canonical IV"' failed.

[sjoerdmeijer]

CC: @fhahn

[sjoerdmeijer]

This shows a different error on compiler explorer:

https://godbolt.org/z/WYxq3nq4q

I guess that's because of some local changes to force loop interchange.

Action is on me to provide an IR reproducer.

[sjoerdmeijer]

I was just picking this up, but just noticed that with a recent trunk build, there's now a different error for this input:

#0 0x0000aaaaaf3b4fd0 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (bin/clang+++0x4914fd0)
 #1 0x0000aaaaaf3b2a68 llvm::sys::RunSignalHandlers() (bin/clang+++0x4912a68)
 #2 0x0000aaaaaf3080b0 CrashRecoverySignalHandler(int) CrashRecoveryContext.cpp:0:0
 #3 0x0000fffff7fb09d0 (linux-vdso.so.1+0x9d0)
 #4 0x0000fffff7a1f200 __pthread_kill_implementation ./nptl/./nptl/pthread_kill.c:44:76
 #5 0x0000fffff79da67c gsignal ./signal/../sysdeps/posix/raise.c:27:6
 #6 0x0000fffff79c7130 abort ./stdlib/./stdlib/abort.c:81:7
 #7 0x0000fffff79d3fd0 __assert_fail_base ./assert/./assert/assert.c:89:7
 #8 0x0000fffff79d4040 __assert_perror_fail ./assert/./assert/assert-perr.c:31:1
 #9 0x0000aaaab06bf480 preparePlanForEpilogueVectorLoop(llvm::VPlan&, llvm::Loop*, llvm::DenseMap<llvm::SCEV const*, llvm::Value*, llvm::DenseMapInfo<llvm::SCEV const*, void>, llvm::detail::DenseMapPair<llvm::SCEV const*, llvm::Value*> > const&, llvm::EpilogueLoopVectorizationInfo const&) LoopVectorize.cpp:0:0

FYI: @fhahn , @david-arm, this now seems to crash in EpilogueLoopVectorizationInfo, so I guess there's some interaction going on with your work in this area?

[fhahn]

Locally this crashes from me with the same assertion as #149726, should be fixed by #149789

[fhahn]

This should now be fixed. It's not crashing on latest main: https://godbolt.org/z/dfMsc89E1 (this is basically https://godbolt.org/z/WYxq3nq4q with a whitespace edit, as the godbolt seems to have cached the previous result + crash)