[PATCH] D150347: [AMDGPU] Improve abs modifier usage

[Thomas Symalla via Phabricator via llvm-commits]

tsymalla marked an inline comment as done.
tsymalla added inline comments.


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Comment at: llvm/test/CodeGen/AMDGPU/andorbitset.ll:56
 ; SI-NOT:   %bb.1:
-; SI:       s_bitset0_b32 s{{[0-9]+}}, 31
+; SI:       s_and_b32 s{{[0-9]+}}, s{{[0-9]+}}, 0x7fffffff
 define void @bitset_verifier_error() local_unnamed_addr #0 {
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foad wrote:
> I guess we no longer form s_bitset because the s_and uses two different registers? That means that this is no longer testing the original bug from D85307. Maybe change the test to use `and i32 undef, 0xBFFFFFFF` (clear bit 30) instead of fabs, so that your new optimization won't spoil it?
Yes, this is, because two different SGPRs are being used. Thanks for the suggestion. I think it makes sense, but unfortunately, it doesn't work. In the original test, the fabs calls are kept until we reach isel - which is a bit strange, because the fabs calls are trivially redundant semantically.

```
  %i = call float @llvm.fabs.f32(float undef) #6
  %i1 = bitcast float %i to i32
  store i32 %i1, ptr addrspace(1) @gv, align 4
  %0 = call float @llvm.fabs.f32(float undef) #6
```

However, when using `and` instead, the expressions are eliminated early.


Repository:
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  https://reviews.llvm.org/D150347/new/

https://reviews.llvm.org/D150347