[llvm] [RISCV] Move RISCVDeadRegisterDefinitions to post regalloc (PR #90636)
Luke Lau via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 30 11:17:05 PDT 2024
https://github.com/lukel97 updated https://github.com/llvm/llvm-project/pull/90636
>From 93868c52d263dc5deac57cf85895b886f789385e Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Tue, 30 Apr 2024 20:45:02 +0800
Subject: [PATCH 1/2] [RISCV] Move RISCVDeadRegisterDefinitions to post
regalloc
The original patch mentions that it may reduce register pressure and improve register allocation, but I believe the register allocator already accounts for dead defs hence why this almost an NFC.
There are no differences on llvm-test-suite or SPEC CPU 2017 with -O3 and -march=rv64gv, just one case in the in-tree tests where a vsetvli output VL is now marked as dead after phi elimination.
The motivation for this is to slightly simplify how we handle vleff with post (vector) regalloc in #70549, by keeping GPR defs virtual where possible.
---
llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp | 4 +---
llvm/lib/Target/RISCV/RISCVTargetMachine.cpp | 6 +++---
llvm/test/CodeGen/RISCV/O3-pipeline.ll | 2 +-
llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll | 4 ++--
4 files changed, 7 insertions(+), 9 deletions(-)
diff --git a/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp b/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
index df607236f7d56f..fd6708c44e7720 100644
--- a/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
+++ b/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
@@ -77,10 +77,8 @@ bool RISCVDeadRegisterDefinitions::runOnMachineFunction(MachineFunction &MF) {
LLVM_DEBUG(dbgs() << " Ignoring, def is tied operand.\n");
continue;
}
- // We should not have any relevant physreg defs that are replacable by
- // zero before register allocation. So we just check for dead vreg defs.
Register Reg = MO.getReg();
- if (!Reg.isVirtual() || (!MO.isDead() && !MRI->use_nodbg_empty(Reg)))
+ if (!MO.isDead() && !MRI->use_nodbg_empty(Reg))
continue;
LLVM_DEBUG(dbgs() << " Dead def operand #" << I << " in:\n ";
MI.print(dbgs()));
diff --git a/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp b/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
index 0876f46728a10c..d4978abf205f53 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetMachine.cpp
@@ -536,9 +536,6 @@ void RISCVPassConfig::addPreRegAlloc() {
if (TM->getOptLevel() != CodeGenOptLevel::None)
addPass(createRISCVMergeBaseOffsetOptPass());
addPass(createRISCVInsertVSETVLIPass());
- if (TM->getOptLevel() != CodeGenOptLevel::None &&
- EnableRISCVDeadRegisterElimination)
- addPass(createRISCVDeadRegisterDefinitionsPass());
addPass(createRISCVInsertReadWriteCSRPass());
addPass(createRISCVInsertWriteVXRMPass());
}
@@ -553,6 +550,9 @@ void RISCVPassConfig::addPostRegAlloc() {
if (TM->getOptLevel() != CodeGenOptLevel::None &&
EnableRedundantCopyElimination)
addPass(createRISCVRedundantCopyEliminationPass());
+ if (TM->getOptLevel() != CodeGenOptLevel::None &&
+ EnableRISCVDeadRegisterElimination)
+ addPass(createRISCVDeadRegisterDefinitionsPass());
}
yaml::MachineFunctionInfo *
diff --git a/llvm/test/CodeGen/RISCV/O3-pipeline.ll b/llvm/test/CodeGen/RISCV/O3-pipeline.ll
index 4121d111091117..174996b9c10b00 100644
--- a/llvm/test/CodeGen/RISCV/O3-pipeline.ll
+++ b/llvm/test/CodeGen/RISCV/O3-pipeline.ll
@@ -116,7 +116,6 @@
; CHECK-NEXT: RISC-V Pre-RA pseudo instruction expansion pass
; CHECK-NEXT: RISC-V Merge Base Offset
; CHECK-NEXT: RISC-V Insert VSETVLI pass
-; CHECK-NEXT: RISC-V Dead register definitions
; CHECK-NEXT: RISC-V Insert Read/Write CSR Pass
; CHECK-NEXT: RISC-V Insert Write VXRM Pass
; CHECK-NEXT: Detect Dead Lanes
@@ -153,6 +152,7 @@
; CHECK-NEXT: Machine Copy Propagation Pass
; CHECK-NEXT: Machine Loop Invariant Code Motion
; CHECK-NEXT: RISC-V Redundant Copy Elimination
+; CHECK-NEXT: RISC-V Dead register definitions
; CHECK-NEXT: Remove Redundant DEBUG_VALUE analysis
; CHECK-NEXT: Fixup Statepoint Caller Saved
; CHECK-NEXT: PostRA Machine Sink
diff --git a/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll b/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
index 4ff2fc7a5fff5d..088d121564bc96 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
@@ -88,13 +88,13 @@ define <vscale x 1 x double> @test3(i64 %avl, i8 zeroext %cond, <vscale x 1 x do
; CHECK: # %bb.0: # %entry
; CHECK-NEXT: beqz a1, .LBB2_2
; CHECK-NEXT: # %bb.1: # %if.then
-; CHECK-NEXT: vsetvli a0, a0, e64, m1, ta, ma
+; CHECK-NEXT: vsetvli zero, a0, e64, m1, ta, ma
; CHECK-NEXT: vfadd.vv v9, v8, v9
; CHECK-NEXT: vfmul.vv v8, v9, v8
; CHECK-NEXT: # implicit-def: $x10
; CHECK-NEXT: ret
; CHECK-NEXT: .LBB2_2: # %if.else
-; CHECK-NEXT: vsetvli a0, a0, e64, m1, ta, ma
+; CHECK-NEXT: vsetvli zero, a0, e64, m1, ta, ma
; CHECK-NEXT: vfsub.vv v9, v8, v9
; CHECK-NEXT: vfmul.vv v8, v9, v8
; CHECK-NEXT: # implicit-def: $x10
>From f5b00273085b6ab2fa153d7f8521314ad9af3170 Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Wed, 1 May 2024 02:16:27 +0800
Subject: [PATCH 2/2] Remove MRI since it's no longer used
---
llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp b/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
index fd6708c44e7720..d93a6428d89487 100644
--- a/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
+++ b/llvm/lib/Target/RISCV/RISCVDeadRegisterDefinitions.cpp
@@ -51,7 +51,6 @@ bool RISCVDeadRegisterDefinitions::runOnMachineFunction(MachineFunction &MF) {
if (skipFunction(MF.getFunction()))
return false;
- const MachineRegisterInfo *MRI = &MF.getRegInfo();
const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
LLVM_DEBUG(dbgs() << "***** RISCVDeadRegisterDefinitions *****\n");
@@ -77,8 +76,7 @@ bool RISCVDeadRegisterDefinitions::runOnMachineFunction(MachineFunction &MF) {
LLVM_DEBUG(dbgs() << " Ignoring, def is tied operand.\n");
continue;
}
- Register Reg = MO.getReg();
- if (!MO.isDead() && !MRI->use_nodbg_empty(Reg))
+ if (!MO.isDead())
continue;
LLVM_DEBUG(dbgs() << " Dead def operand #" << I << " in:\n ";
MI.print(dbgs()));
@@ -88,7 +86,6 @@ bool RISCVDeadRegisterDefinitions::runOnMachineFunction(MachineFunction &MF) {
continue;
}
MO.setReg(RISCV::X0);
- MO.setIsDead();
LLVM_DEBUG(dbgs() << " Replacing with zero register. New:\n ";
MI.print(dbgs()));
++NumDeadDefsReplaced;
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