[llvm] [CodeGen] Fix handling dead redefs in finalizeBundle (PR #157427)
Jay Foad via llvm-commits
llvm-commits at lists.llvm.org
Mon Sep 8 04:16:54 PDT 2025
https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/157427
A dead redefinition should override any earlier non-dead definition
inside a bundle.
Also remove KilledDefSet since it can be folded into DeadDefSet.
>From 39f358f319d926b2709fc0feb434a60f3f6941c7 Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Mon, 8 Sep 2025 11:54:25 +0100
Subject: [PATCH 1/2] Precommit test
---
llvm/test/CodeGen/AMDGPU/finalizebundle.mir | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/llvm/test/CodeGen/AMDGPU/finalizebundle.mir b/llvm/test/CodeGen/AMDGPU/finalizebundle.mir
index 46ca6d347781e..a49c58ed33d94 100644
--- a/llvm/test/CodeGen/AMDGPU/finalizebundle.mir
+++ b/llvm/test/CodeGen/AMDGPU/finalizebundle.mir
@@ -16,3 +16,21 @@ body: |
$vgpr2_vgpr3 = V_LSHLREV_B64_pseudo_e32 1, $vgpr0_vgpr1, implicit $exec
$vgpr3_vgpr4 = V_LSHLREV_B64_pseudo_e32 1, $vgpr1_vgpr2, implicit $exec
...
+
+---
+name: test_dead_redef
+body: |
+ bb.0:
+ liveins: $vgpr0
+ ; CHECK-LABEL: name: test_dead_redef
+ ; CHECK: liveins: $vgpr0
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: BUNDLE implicit-def $vgpr1, implicit-def $vgpr0, implicit $vgpr0, implicit $exec {
+ ; CHECK-NEXT: $vgpr1 = V_MOV_B32_e32 $vgpr0, implicit $exec
+ ; CHECK-NEXT: $vgpr0 = V_MOV_B32_e32 internal $vgpr1, implicit $exec
+ ; CHECK-NEXT: dead $vgpr1 = V_MOV_B32_e32 internal $vgpr0, implicit $exec
+ ; CHECK-NEXT: }
+ $vgpr1 = V_MOV_B32_e32 $vgpr0, implicit $exec
+ $vgpr0 = V_MOV_B32_e32 $vgpr1, implicit $exec
+ dead $vgpr1 = V_MOV_B32_e32 $vgpr0, implicit $exec
+...
>From 4ed7239c2bc7d2b0f6253dce35fb1f09d50c84ab Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Mon, 8 Sep 2025 11:56:41 +0100
Subject: [PATCH 2/2] [CodeGen] Fix handling dead redefs in finalizeBundle
A dead redefinition should override any earlier non-dead definition
inside a bundle.
Also remove KilledDefSet since it can be folded into DeadDefSet.
---
llvm/lib/CodeGen/MachineInstrBundle.cpp | 16 +++++++---------
.../AArch64/blr-bti-preserves-operands.mir | 2 +-
llvm/test/CodeGen/AMDGPU/finalizebundle.mir | 2 +-
3 files changed, 9 insertions(+), 11 deletions(-)
diff --git a/llvm/lib/CodeGen/MachineInstrBundle.cpp b/llvm/lib/CodeGen/MachineInstrBundle.cpp
index 5830ecfe4aa20..da29ffc9d2fed 100644
--- a/llvm/lib/CodeGen/MachineInstrBundle.cpp
+++ b/llvm/lib/CodeGen/MachineInstrBundle.cpp
@@ -133,7 +133,6 @@ void llvm::finalizeBundle(MachineBasicBlock &MBB,
SmallSetVector<Register, 32> LocalDefs;
BitVector LocalDefsP(TRI->getNumRegUnits());
SmallSet<Register, 8> DeadDefSet;
- SmallSet<Register, 16> KilledDefSet;
SmallSetVector<Register, 8> ExternUses;
SmallSet<Register, 8> KilledUseSet;
SmallSet<Register, 8> UndefUseSet;
@@ -151,7 +150,7 @@ void llvm::finalizeBundle(MachineBasicBlock &MBB,
MO.setIsInternalRead();
if (MO.isKill()) {
// Internal def is now killed.
- KilledDefSet.insert(Reg);
+ DeadDefSet.insert(Reg);
}
} else {
if (ExternUses.insert(Reg)) {
@@ -171,19 +170,18 @@ void llvm::finalizeBundle(MachineBasicBlock &MBB,
continue;
if (LocalDefs.insert(Reg)) {
- if (MO.isDead())
- DeadDefSet.insert(Reg);
- else if (Reg.isPhysical())
+ if (!MO.isDead() && Reg.isPhysical()) {
for (MCRegUnit Unit : TRI->regunits(Reg.asMCReg()))
LocalDefsP.set(Unit);
+ }
} else {
- // Re-defined inside the bundle, it's no longer killed.
- KilledDefSet.erase(Reg);
if (!MO.isDead()) {
- // Previously defined but dead.
+ // Re-defined inside the bundle, it's no longer dead.
DeadDefSet.erase(Reg);
}
}
+ if (MO.isDead())
+ DeadDefSet.insert(Reg);
}
// Set FrameSetup/FrameDestroy for the bundle. If any of the instructions
@@ -196,7 +194,7 @@ void llvm::finalizeBundle(MachineBasicBlock &MBB,
for (Register Reg : LocalDefs) {
// If it's not live beyond end of the bundle, mark it dead.
- bool isDead = DeadDefSet.contains(Reg) || KilledDefSet.contains(Reg);
+ bool isDead = DeadDefSet.contains(Reg);
MIB.addReg(Reg, getDefRegState(true) | getDeadRegState(isDead) |
getImplRegState(true));
}
diff --git a/llvm/test/CodeGen/AArch64/blr-bti-preserves-operands.mir b/llvm/test/CodeGen/AArch64/blr-bti-preserves-operands.mir
index f41e590c870a4..a4a392c41ec9a 100644
--- a/llvm/test/CodeGen/AArch64/blr-bti-preserves-operands.mir
+++ b/llvm/test/CodeGen/AArch64/blr-bti-preserves-operands.mir
@@ -8,7 +8,7 @@
# The arguments to the call must become implicit arguments, because the branch
# only expects to get 1 explicit operand which is the branch target.
-# CHECK: BUNDLE implicit-def $lr, implicit-def $sp, implicit $sp, implicit $x0, implicit $w1 {
+# CHECK: BUNDLE implicit-def dead $lr, implicit-def $sp, implicit $sp, implicit $x0, implicit $w1 {
# CHECK: BL @_setjmp, csr_aarch64_aapcs, implicit-def $lr, implicit $sp, implicit $x0, implicit $w1, implicit-def dead $lr, implicit $sp, implicit-def $sp
# CHECK: HINT 36
# CHECK: }
diff --git a/llvm/test/CodeGen/AMDGPU/finalizebundle.mir b/llvm/test/CodeGen/AMDGPU/finalizebundle.mir
index a49c58ed33d94..0548bcf304c32 100644
--- a/llvm/test/CodeGen/AMDGPU/finalizebundle.mir
+++ b/llvm/test/CodeGen/AMDGPU/finalizebundle.mir
@@ -25,7 +25,7 @@ body: |
; CHECK-LABEL: name: test_dead_redef
; CHECK: liveins: $vgpr0
; CHECK-NEXT: {{ $}}
- ; CHECK-NEXT: BUNDLE implicit-def $vgpr1, implicit-def $vgpr0, implicit $vgpr0, implicit $exec {
+ ; CHECK-NEXT: BUNDLE implicit-def dead $vgpr1, implicit-def $vgpr0, implicit $vgpr0, implicit $exec {
; CHECK-NEXT: $vgpr1 = V_MOV_B32_e32 $vgpr0, implicit $exec
; CHECK-NEXT: $vgpr0 = V_MOV_B32_e32 internal $vgpr1, implicit $exec
; CHECK-NEXT: dead $vgpr1 = V_MOV_B32_e32 internal $vgpr0, implicit $exec
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