[clang] Crash with O2 optimization flag

[cardigan1008]

I compiled this code with -O2 flag and it crashed. The code is:

#include <stdint.h>
long a, c;
unsigned d;
int32_t g;
uint8_t h[];
long b(long p1, long k) {
  long e = k;
  int b = 0;
  while (e) {
    e /= 10;
    b++;
  }
  for (int f = 0; f < b; f++)
    p1 *= 10;
  a = p1 + k;
  return a;
}
long i(int p1, int, int l) {
  int j = l / p1;
  for (int f = 0; f < p1; f++) {
    if (d > l)
      break;
    c = d += j;
  }
}
uint32_t m() {
  for (g = 8; b(35, 46) - 3546 + g >= 0; g--)
    ;
  h[i(g + 1, 0, -4294967221)];
}

The crash is: clang: /root/llvm-project/llvm/include/llvm/Support/Casting.h:662: decltype(auto) llvm::dyn_cast(From*) [with To = llvm::BinaryOperator; From = llvm::Instruction]: Assertion `detail::isPresent(Val) && "dyn_cast on a non-existent value"' failed.

The details can be found here: https://godbolt.org/z/37WsGxMcv

[shafik]

Looks like a regression, does not crash in clang-18: https://godbolt.org/z/1zYqs3sbz

[dtcxzyw]

Reproducer: https://godbolt.org/z/bbdhPxx5E

; bin/opt -passes=indvars reduced.ll -S
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"

define i32 @m() {
entry:
  %div.i4 = sdiv i32 1, 0
  br label %for.body.i6

for.body.i6:                                      ; preds = %if.end.i, %entry
  %add57.i = phi i32 [ %add.i7, %if.end.i ], [ 0, %entry ]
  br i1 true, label %i.exit, label %if.end.i

if.end.i:                                         ; preds = %for.body.i6
  %add.i7 = add i32 %add57.i, %div.i4
  %conv.i = zext i32 %add57.i to i64
  store i64 %conv.i, ptr null, align 8
  br label %for.body.i6

i.exit:                                           ; preds = %for.body.i6
  ret i32 0
}

cc @nikic

[DimitryAndric]

This regressed with llvmorg-19-init-02822-g4db93e5 ("[IndVars] Recompute flags if needed in widenIVUse of IV increment. (#82352)") by @fhahn.

[nikic]

/cherry-pick c9a5e1b

[llvmbot]

/pull-request #106892