[PATCH] D82370: [AMDGPU] Rework SCC copy

[Piotr Sobczak via Phabricator via llvm-commits]

piotr added inline comments.


================
Comment at: llvm/lib/Target/AMDGPU/SIInstrInfo.cpp:674-675
+
+    // We only care about the low bit here.
+    if (AMDGPU::SReg_64RegClass.contains(SrcReg)) {
+      SrcReg = RI.getSubReg(SrcReg, AMDGPU::sub0);
----------------
arsenm wrote:
> I think you should never end up in this situation to begin with. Maybe this should be a verifier error instead?
This comes directly from the isel, so I guess is one of the peculiarities of flag registers handling.

===== Instruction selection ends
...
            t89: i1 = V_CMP_LT_U64_e64 t103, t144 
          t131: ch,glue = CopyToReg t0, Register:i1 $scc, t89
        t86: i32 = S_CSELECT_B32 t55, t141, t131:1
...

*** MachineFunction at end of ISel ***
...
  %46:sreg_64 = V_CMP_LT_U64_e64 %27:sreg_64, %47:vreg_64, implicit $exec
  $scc = COPY %46:sreg_64
  %48:sreg_32 = S_CSELECT_B32 killed %44:sreg_32, %42:sreg_32, implicit $scc
...






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  https://reviews.llvm.org/D82370/new/

https://reviews.llvm.org/D82370