[PATCH] D72636: Cancelling out G_MERGE_VALUES/G_UNMERGE pairs sometimes needs a copy

[Daniel Sanders via Phabricator via llvm-commits]

dsanders updated this revision to Diff 237796.
dsanders added a comment.

+Testcase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72636/new/

https://reviews.llvm.org/D72636

Files:
  llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
  llvm/test/CodeGen/AArch64/GlobalISel/legalize-merge-values.mir


Index: llvm/test/CodeGen/AArch64/GlobalISel/legalize-merge-values.mir
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/legalize-merge-values.mir
+++ llvm/test/CodeGen/AArch64/GlobalISel/legalize-merge-values.mir
@@ -25,3 +25,40 @@
     %4:_(s64) = G_ANYEXT %3
     $x0 = COPY %4
 ...
+
+---
+name:            cancel_into_nothing
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: cancel_into_nothing
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $w1
+    ; CHECK: $w10 = COPY [[COPY]](s32)
+    ; CHECK: $w11 = COPY [[COPY1]](s32)
+    %0:_(s32) = COPY $w0
+    %1:_(s32) = COPY $w1
+    %2:_(s64) = G_MERGE_VALUES %0, %1
+    %3:_(s32), %4:_(s32) = G_UNMERGE_VALUES %2
+    $w10 = COPY %3
+    $w11 = COPY %4
+...
+
+---
+name:            cancel_into_copy
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: cancel_into_copy
+    ; CHECK: [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+    ; CHECK: [[COPY1:%[0-9]+]]:_(s32) = COPY $w1
+    ; CHECK: [[COPY2:%[0-9]+]]:gpr32sp(s32) = COPY [[COPY]](s32)
+    ; CHECK: [[ADDWri:%[0-9]+]]:gpr32sp(s32) = ADDWri [[COPY2]](s32), 1, 0
+    ; CHECK: $w10 = COPY [[COPY2]](s32)
+    ; CHECK: $w11 = COPY [[COPY1]](s32)
+    %0:_(s32) = COPY $w0
+    %1:_(s32) = COPY $w1
+    %2:_(s64) = G_MERGE_VALUES %0, %1
+    %3:gpr32sp(s32), %4:_(s32) = G_UNMERGE_VALUES %2
+    %5:gpr32sp(s32) = ADDWri %3:gpr32sp(s32), 1, 0
+    $w10 = COPY %3
+    $w11 = COPY %4
+...
Index: llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
===================================================================
--- llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
+++ llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
@@ -396,7 +396,15 @@
 
       for (unsigned Idx = 0; Idx < NumDefs; ++Idx) {
         Register NewDef = MergeI->getOperand(Idx + 1).getReg();
-        MRI.replaceRegWith(MI.getOperand(Idx).getReg(), NewDef);
+        Register OldReg = MI.getOperand(Idx).getReg();
+        auto *OldRC = MRI.getRegClassOrNull(OldReg);
+        auto *NewRC = MRI.getRegClassOrNull(NewDef);
+        if ((!OldRC && !NewRC) || (OldRC && NewRC && OldRC == NewRC))
+          MRI.replaceRegWith(OldReg, NewDef);
+        else {
+          Builder.setInstr(MI);
+          Builder.buildInstr(TargetOpcode::COPY, {OldReg}, {NewDef});
+        }
         UpdatedDefs.push_back(NewDef);
       }
     }


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