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[MCP] Disable BackwardCopyPropagateBlock for copies with implicit registers. #137687

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Merged
merged 2 commits into from
May 8, 2025
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[MCP] Disable BackwardCopyPropagateBlock for copies with implicit registers. #137687

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topperc Apr 28, 2025
e0a7a58
[MCP] Disable BackwardCopyPropagateBlock for copies with implicit reg…
topperc Apr 28, 2025
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2 changes: 1 addition & 1 deletion llvm/lib/CodeGen/MachineCopyPropagation.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1200,7 +1200,7 @@ void MachineCopyPropagation::BackwardCopyPropagateBlock(
// Ignore non-trivial COPYs.
std::optional<DestSourcePair> CopyOperands =
isCopyInstr(MI, *TII, UseCopyInstr);
if (CopyOperands) {
if (CopyOperands && MI.getNumImplicitOperands() == 0) {
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I thought isCopyInstr was already filtering out these hard cases

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I guess it does in the target instruction implementations, not the base copy handling

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Might as well just not use isCopyInstr, you're probably filtering out cases the target code decided are OK

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For RISC-V, we want to support the canonical copy instruction that appears after ExpandPostRAPseudos, "ADDI rd, rs, 0". What are you suggesting we use here instead of isCopyInstr?

Register DefReg = CopyOperands->Destination->getReg();
Register SrcReg = CopyOperands->Source->getReg();

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21 changes: 21 additions & 0 deletions llvm/test/CodeGen/SystemZ/pr137687.mir
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@@ -0,0 +1,21 @@
# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
# RUN: llc %s -mtriple=s390x-unknown-linux-gnu -run-pass=machine-cp -verify-machineinstrs -o - | FileCheck %s

---
name: t
tracksRegLiveness: true
noPhis: true
isSSA: false
noVRegs: true
hasFakeUses: false
tracksDebugUserValues: true
body: |
bb.0:
; CHECK-LABEL: name: t
; CHECK: renamable $r14d = LLILL 0
; CHECK-NEXT: renamable $r12d = COPY killed renamable $r14d, implicit-def $r12q
; CHECK-NEXT: Return implicit $r12q
renamable $r14d = LLILL 0
renamable $r12d = COPY killed renamable $r14d, implicit-def $r12q
Return implicit $r12q
...