[llvm-bugs] [Bug 36304] New: [Regression] sub nsw i32 %x, -1 gets transformed into add i32 %0, 2147483647 illegally

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36304

            Bug ID: 36304
           Summary: [Regression] sub nsw i32 %x, -1 gets transformed into
                    add i32 %0, 2147483647 illegally
           Product: new-bugs
           Version: 6.0
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: arphaman at gmail.com
                CC: llvm-bugs at lists.llvm.org

LLVM transforms the 'sub nsw i32 %x, -1' instruction into 'add i32 %0,
2147483647' illegally.

Reproducer:

$ cat test.cpp

typedef unsigned long size_t;

void *memcpy(void *__dst, const void *__src, size_t __n);

int Execute(int &minSize, char *Output, const char *Input) {
        for (int d=0; d<64; ++d) {
            for (int s=0; s<64; ++s) {
                for (int n=0; n<3; ++n) {
                    size_t len = minSize + (n*0x11389737 & minSize-1);
                    memcpy(Output+d, Input+s, len);
                }
            }
        }
        return 0;
}

$ ~/u/b/bin/clang repr.cpp -S -Xclang -emit-llvm  -O1 -o ir.ll
$ cat ir.ll

Bad pass: "Combine redundant instructions"
...
  %mul = mul nuw nsw i32 %n.028, 288921399
  %sub = add i32 %0, 2147483647
  %and = and i32 %sub, %mul
...

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