[PATCH] D124834: [fastregalloc] Fix bug when undef value is tied to def.

[LuoYuanke via Phabricator via llvm-commits]

LuoYuanke added inline comments.


================
Comment at: llvm/test/CodeGen/X86/fastregalloc-tied-undef.mir:27
+
+    %0:vr128 = PXORrr undef %0, undef %0
+    MOVAPSmr %stack.1, 1, $noreg, 0, $noreg, %0
----------------
craig.topper wrote:
> Was this a synthetic example? It shouldn't be possible to generate a PXORrr like this before register allocation.
I use the following C code to generate the test case. However compiler would generate "%0:vr128 = V_SET0" instead of "%0:vr128 = PXORrr undef %0, undef %0". The real case that I encounter is to generate code to zero the stack slot for AMX configure register. I use "PXORrr" to zero the stack slot, I can change it to "V_SET0" to avoid the issue in fast regalloc. However I think it expose an issue in fast regalloc, so I create a patch for it.

```
#include <immintrin.h>

void foo() {
  __m128 vec[4];
  __m128 m = {0, 0};

  vec[0] = m;
  vec[1] = m;
  vec[2] = m;
  vec[3] = m;
}
```


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124834/new/

https://reviews.llvm.org/D124834