[PATCH] D78430: [InstSimplify] fold and/or of compares with equality to min/max constant

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added inline comments.


================
Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:1689
+  else if (isa<ConstantPointerNull>(Cmp0->getOperand(1)))
+    MinMaxC = APInt::getNullValue(1);
+  else
----------------
The patch transforms this function into `ret false`, which is not correct. If %a = 0x0 and %b = 0x1, the source program should be true.
```
define i1 @f(i8* %a, i8* %b) {
  %c1 = icmp eq i8* %a, null
  %c2 = icmp slt i8* %a, %b
  %r = and i1 %c1, %c2
  ret i1 %r
}
```
And I think this miscompilation is related with assigning 1-bit integer in this line.
The line 1713 `MinMaxC += APInt::getSignedMinValue(MinMaxC.getBitWidth());` will make `MinMaxC` full of one bits, and it makes if branch at line 1716 taken.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D78430/new/

https://reviews.llvm.org/D78430