[llvm] AArch64: Skip analyzeCompare for subregister uses (PR #141654)
Matt Arsenault via llvm-commits
llvm-commits at lists.llvm.org
Tue May 27 11:35:21 PDT 2025
https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/141654
The API is broken and doesn't provide a way to report the used
subregister, so it's unsafe to use. This will produce illegal
folds if the subregister is silently dropped.
>From acd579ef56f1b493349997a6be9a21c4bea7ec5a Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Tue, 28 Jan 2025 19:42:09 +0700
Subject: [PATCH] AArch64: Skip analyzeCompare for subregister uses
The API is broken and doesn't provide a way to report the used
subregister, so it's unsafe to use. This will produce illegal
folds if the subregister is silently dropped.
---
llvm/lib/Target/AArch64/AArch64InstrInfo.cpp | 11 ++-
...peephole-opt-analyzeCompare-subreg-use.mir | 67 +++++++++++++++++++
2 files changed, 77 insertions(+), 1 deletion(-)
create mode 100644 llvm/test/CodeGen/AArch64/peephole-opt-analyzeCompare-subreg-use.mir
diff --git a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
index d6225bca233b6..f95d7b7ac8c73 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
+++ b/llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
@@ -1277,8 +1277,9 @@ bool AArch64InstrInfo::analyzeCompare(const MachineInstr &MI, Register &SrcReg,
int64_t &CmpValue) const {
// The first operand can be a frame index where we'd normally expect a
// register.
+ // FIXME: Pass subregisters out of analyzeCompare
assert(MI.getNumOperands() >= 2 && "All AArch64 cmps should have 2 operands");
- if (!MI.getOperand(1).isReg())
+ if (!MI.getOperand(1).isReg() || MI.getOperand(1).getSubReg())
return false;
switch (MI.getOpcode()) {
@@ -1288,6 +1289,9 @@ bool AArch64InstrInfo::analyzeCompare(const MachineInstr &MI, Register &SrcReg,
case AArch64::PTEST_PP_ANY:
SrcReg = MI.getOperand(0).getReg();
SrcReg2 = MI.getOperand(1).getReg();
+ if (MI.getOperand(2).getSubReg())
+ return false;
+
// Not sure about the mask and value for now...
CmpMask = ~0;
CmpValue = 0;
@@ -1307,6 +1311,11 @@ bool AArch64InstrInfo::analyzeCompare(const MachineInstr &MI, Register &SrcReg,
// Replace SUBSWrr with SUBWrr if NZCV is not used.
SrcReg = MI.getOperand(1).getReg();
SrcReg2 = MI.getOperand(2).getReg();
+
+ // FIXME: Pass subregisters out of analyzeCompare
+ if (MI.getOperand(2).getSubReg())
+ return false;
+
CmpMask = ~0;
CmpValue = 0;
return true;
diff --git a/llvm/test/CodeGen/AArch64/peephole-opt-analyzeCompare-subreg-use.mir b/llvm/test/CodeGen/AArch64/peephole-opt-analyzeCompare-subreg-use.mir
new file mode 100644
index 0000000000000..c9d6bc7cc8f87
--- /dev/null
+++ b/llvm/test/CodeGen/AArch64/peephole-opt-analyzeCompare-subreg-use.mir
@@ -0,0 +1,67 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=aarch64-- -run-pass=peephole-opt -o - %s | FileCheck %s
+
+# Make sure that analyzeCompare doesn't produce illegal folds due to
+# ignoring the subregister index on the use operands.
+
+---
+name: analyze_compare_subreg_use_lhs
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $x0, $x1
+
+ ; CHECK-LABEL: name: analyze_compare_subreg_use_lhs
+ ; CHECK: liveins: $x0, $x1
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr64 = COPY $x1
+ ; CHECK-NEXT: [[COPY1:%[0-9]+]]:gpr64 = COPY $x0
+ ; CHECK-NEXT: [[COPY2:%[0-9]+]]:gpr32 = COPY $wzr
+ ; CHECK-NEXT: [[SUBSWrr:%[0-9]+]]:gpr32 = SUBSWrr [[COPY]].sub_32, [[COPY2]], implicit-def dead $nzcv
+ ; CHECK-NEXT: [[DEF:%[0-9]+]]:gpr64all = IMPLICIT_DEF
+ ; CHECK-NEXT: [[INSERT_SUBREG:%[0-9]+]]:gpr64 = INSERT_SUBREG [[DEF]], killed [[SUBSWrr]], %subreg.sub_32
+ ; CHECK-NEXT: [[RORVXr:%[0-9]+]]:gpr64 = RORVXr [[COPY1]], killed [[INSERT_SUBREG]]
+ ; CHECK-NEXT: $x0 = COPY [[RORVXr]]
+ ; CHECK-NEXT: RET_ReallyLR implicit $x0
+ %0:gpr64 = COPY $x1
+ %1:gpr64 = COPY $x0
+ %2:gpr32 = COPY $wzr
+ %3:gpr32 = SUBSWrr %0.sub_32, %2, implicit-def dead $nzcv
+ %4:gpr64all = IMPLICIT_DEF
+ %5:gpr64 = INSERT_SUBREG %4, killed %3, %subreg.sub_32
+ %6:gpr64 = RORVXr %1, killed %5
+ $x0 = COPY %6
+ RET_ReallyLR implicit $x0
+
+...
+
+---
+name: analyze_compare_subreg_use_rhs
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $x0, $x1
+
+ ; CHECK-LABEL: name: analyze_compare_subreg_use_rhs
+ ; CHECK: liveins: $x0, $x1
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr64 = COPY $x1
+ ; CHECK-NEXT: [[COPY1:%[0-9]+]]:gpr64 = COPY $x0
+ ; CHECK-NEXT: [[COPY2:%[0-9]+]]:gpr32 = COPY $wzr
+ ; CHECK-NEXT: [[SUBSWrr:%[0-9]+]]:gpr32 = SUBSWrr [[COPY2]], [[COPY]].sub_32, implicit-def dead $nzcv
+ ; CHECK-NEXT: [[DEF:%[0-9]+]]:gpr64all = IMPLICIT_DEF
+ ; CHECK-NEXT: [[INSERT_SUBREG:%[0-9]+]]:gpr64 = INSERT_SUBREG [[DEF]], killed [[SUBSWrr]], %subreg.sub_32
+ ; CHECK-NEXT: [[RORVXr:%[0-9]+]]:gpr64 = RORVXr [[COPY1]], killed [[INSERT_SUBREG]]
+ ; CHECK-NEXT: $x0 = COPY [[RORVXr]]
+ ; CHECK-NEXT: RET_ReallyLR implicit $x0
+ %0:gpr64 = COPY $x1
+ %1:gpr64 = COPY $x0
+ %2:gpr32 = COPY $wzr
+ %3:gpr32 = SUBSWrr %2, %0.sub_32, implicit-def dead $nzcv
+ %4:gpr64all = IMPLICIT_DEF
+ %5:gpr64 = INSERT_SUBREG %4, killed %3, %subreg.sub_32
+ %6:gpr64 = RORVXr %1, killed %5
+ $x0 = COPY %6
+ RET_ReallyLR implicit $x0
+
+...
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