| Issue |
131478
|
| Summary |
[MachineCopyProp, SystemZ] "Using an undefined physical register"
|
| Labels |
backend:SystemZ,
llvm:codegen
|
| Assignees |
|
| Reporter |
JonPsson1
|
MachineVerifier reported *** Bad machine code: Using an undefined physical register ***.
git bisect shows
```
commit 2def1c4 (HEAD, refs/bisect/bad):
[RISCV][MCP] Remove redundant move from tail duplication (#89865)
Tail duplication will generate the redundant move before return. It is
because the MachineCopyPropogation can't recognize COPY after post-RA
pseudoExpand.
This patch make MachineCopyPropogation recognize `%0 = ADDI %1, 0` as
COPY
diff --git a/llvm/lib/CodeGen/MachineCopyPropagation.cpp b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
index b34e0939d1c7..fab36f4858e0 100644
--- a/llvm/lib/CodeGen/MachineCopyPropagation.cpp
+++ b/llvm/lib/CodeGen/MachineCopyPropagation.cpp
@@ -1053,7 +1053,7 @@ void MachineCopyPropagation::BackwardCopyPropagateBlock(
// Ignore non-trivial COPYs.
std::optional<DestSourcePair> CopyOperands =
isCopyInstr(MI, *TII, UseCopyInstr);
- if (CopyOperands && MI.getNumOperands() == 2) {
+ if (CopyOperands) {
Register DefReg = CopyOperands->Destination->getReg();
Register SrcReg = CopyOperands->Source->getReg();
```
This changes the result of MachineCP on this test case like:
```
old <> failing
*** IR Dump After Machine Copy Propagation Pass (machine-cp) ***
renamable $r14d = LLILL 0 | renamable $r12d = LLILL 0
renamable $r12d = COPY killed renamable $r14d, implicit-def $r12q <
renamable $r14l = LMux %fixed-stack.11, 4, $noreg :: (load (s32) fro renamable $r14l = LMux %fixed-stack.11, 4, $noreg :: (load (s32) fro
renamable $r14l = LLHRMux killed renamable $r14l renamable $r14l = LLHRMux killed renamable $r14l
renamable $r3l = LMux killed renamable $r3d, 12, $noreg :: (load (s3 renamable $r3l = LMux killed renamable $r3d, 12, $noreg :: (load (s3
renamable $r11d = LGFR killed renamable $r3l, implicit-def $r10q renamable $r11d = LGFR killed renamable $r3l, implicit-def $r10q
ST128 killed renamable $r10q, %stack.5, 0, $noreg :: (store (s128) i ST128 killed renamable $r10q, %stack.5, 0, $noreg :: (store (s128) i
renamable $r10q = COPY killed renamable $r12q renamable $r10q = COPY killed renamable $r12q
*** IR Dump After Post-RA pseudo instruction expansion pass
renamable $r14d = LLILL 0 | renamable $r12d = LLILL 0
$r12d = LGR killed $r14d, implicit-def $r12q <
renamable $r14l = L $r15d, 380, $noreg :: (load (s32) from %fixed-st renamable $r14l = L $r15d, 380, $noreg :: (load (s32) from %fixed-st
$r14l = LLHR killed $r14l $r14l = LLHR killed $r14l
renamable $r3l = L killed renamable $r3d, 12, $noreg :: (load (s32) renamable $r3l = L killed renamable $r3d, 12, $noreg :: (load (s32)
renamable $r11d = LGFR killed renamable $r3l, implicit-def $r10q renamable $r11d = LGFR killed renamable $r3l, implicit-def $r10q
STG $r10d, $r15d, 184, $noreg, implicit $r10q :: (store (s128) into STG $r10d, $r15d, 184, $noreg, implicit $r10q :: (store (s128) into
STG killed $r11d, $r15d, 192, $noreg, implicit killed $r10q :: (stor STG killed $r11d, $r15d, 192, $noreg, implicit killed $r10q :: (stor
$r10d = LGR killed $r12d, implicit $r12q $r10d = LGR killed $r12d, implicit $r12q
$r11d = LGR killed $r13d, implicit killed $r12q $r11d = LGR killed $r13d, implicit killed $r12q
*** Bad machine code: Using an undefined physical register ***
- function: t
- basic block: %bb.0 (0xade6dc0)
- instruction: $r11d = LGR killed $r13d, implicit killed $r12q
- operand 2: implicit killed $r12q
LLVM ERROR: Found 1 machine code errors.
```
With the LGR (left), there is an implicit-def of $r12q.
In the failing version (right), I see MachineCP propagating a COPY, but while doing so dropping the implicit-def of $r12q:
```
*** IR Dump After Greedy Register Allocator (greedy) ***:
528B %53:gr64bit = LLILL 0
544B undef %58.subreg_h64:gr128bit = COPY %53:gr64bit
636B %57:gr128bit = COPY %58:gr128bit
*** IR Dump After SystemZ Post Rewrite pass (systemz-post-rewrite) ***:
renamable $r14d = LLILL 0
renamable $r12d = COPY killed renamable $r14d, implicit-def $r12q
renamable $r10q = COPY killed renamable $r12q
*** IR Dump After Machine Copy Propagation Pass (machine-cp) ***
renamable $r12d = LLILL 0
renamable $r10q = COPY killed renamable $r12q
*** IR Dump After Post-RA pseudo instruction expansion pass (postrapseudos) ***:
renamable $r12d = LLILL 0
$r10d = LGR killed $r12d, implicit $r12q
$r11d = LGR killed $r13d, implicit killed $r12q
```
*** Bad machine code: $r12q is undefined in last LGR as $r13d never had a definition.
The MIR looks legal up until MachineCP, so maybe something is missing there?
[tc_gr128CopyExp.tar.gz](https://github.com/user-attachments/files/19266599/tc_gr128CopyExp.tar.gz)
llc -mcpu=z15 -O3 -disable-cgp -use-mbpi=false -greedy-reverse-local-assignment -aggressive-machine-cse -misched=ilpmin -verify-machineinstrs ./tc_gr128CopyExp.ll
@BeMg @arsenm @efriedma-quic @asb @jsji @vladimirradosavljevic @uweigand
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