[PATCH] D106053: [CodeGen] Remove pending AssertZext AssertSext in promoting FP_TO_INT

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune added inline comments.


================
Comment at: llvm/test/CodeGen/X86/fptoui-may-overflow.ll:5
+; We can't only generate "cvttps2dq %xmm0, %xmm0" for this function, because
+; there may be overflow case in fptoui. The old DAG optimization will optimize
+; "%f = fptoui <4 x float> %arg to <4 x i8>" to
----------------
According to LangRef (https://llvm.org/docs/LangRef.html#fptoui-to-instruction), the overflow returns `poison` which means that using the value is invalid.

This is analogous to using an uninitialized variable in C/C++; there is no guarantee that the compiled program will have a reasonable behavior.
```
int x; // not initialized
printf("%d", x); // Assume that this printed 0xDEADBEEF
... (don't update x)
printf("%d", x); // There is no guarantee that this will also print 0xDEADBEEF
```


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D106053/new/

https://reviews.llvm.org/D106053