[PATCH] D95432: AMDGPU/GlobalISel: Combine uniform icmp with select

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

This should also apply to conditional branches, but the user doesn't actually matter. This is really a generic combine for (trunc (bool_ext_type bool_producer))



================
Comment at: llvm/lib/Target/AMDGPU/AMDGPUCombine.td:44
+  (defs root:$select, uniform_icmp_select_matchdata:$matchinfo),
+  (match (wip_match_opcode G_SELECT):$select,
+         [{ return RegBankHelper.matchUniformICmpSelect(*${select}, ${matchinfo}); }]),
----------------
The select part here isn't essential, but the matcher here wants a specific opcode. I guess you could bypass the generated combine matcher and just call this combine in a switch, or at least add the relevant G_BRCOND user


================
Comment at: llvm/lib/Target/AMDGPU/AMDGPURegBankCombiner.cpp:90
+              ICMP.getOperand(0), ICMP.getOperand(2), ICMP.getOperand(3));
+  MI.getOperand(1).setReg(MatchInfo.ICmpReg);
+  ICMP.eraseFromParent();
----------------
Changing the instruction without notifying the observer


================
Comment at: llvm/test/CodeGen/AMDGPU/GlobalISel/combine-uniform-icmp-select.mir:37-62
+    ; CHECK: S_ENDPGM 0
+    %4:sgpr(s32) = COPY $sgpr0
+    %5:sgpr(s32) = COPY $sgpr1
+    %6:sgpr(s32) = COPY $sgpr2
+    %7:sgpr(s32) = COPY $sgpr3
+    %8:sgpr(s32) = COPY $sgpr4
+    %9:sgpr(s32) = COPY $sgpr5
----------------
Most of these instructions aren't relevant to the combine. You can also directly emit copies from 64-bit SGPRs even though we emit them normally as separate 32-bit copies


================
Comment at: llvm/test/CodeGen/AMDGPU/GlobalISel/combine-uniform-icmp-select.mir:116-142
+    %9:sgpr(s32) = COPY $sgpr3
+    %10:sgpr(s32) = COPY $sgpr4
+    %11:sgpr(s32) = COPY $sgpr5
+    %12:sgpr(s32) = COPY $sgpr6
+    %13:sgpr(s32) = COPY $sgpr7
+    %14:vgpr(s32) = COPY $vgpr0
+    %15:vgpr(s32) = COPY $vgpr1
----------------
Ditto


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D95432/new/

https://reviews.llvm.org/D95432