[llvm] [RISCV] Fold vmv.v.v into vmerge (PR #151341)
Luke Lau via llvm-commits
llvm-commits at lists.llvm.org
Wed Jul 30 07:09:56 PDT 2025
https://github.com/lukel97 created https://github.com/llvm/llvm-project/pull/151341
We support folding vmv.v.v into its source via the foldVMV_V_V peephole, but currently it requires that the source has a policy operand.
PseudoVMERGEs (as well as add-with-carry/subtract-with-borrow pseudos) don't have a policy operand, and instead just seem to derive TA/TU from whether or not the passthru is undef, since the mask policy doesn't affect them.
This patch allows pseudos without policy operands, given that if there's no policy operand then it will default to TU when the passthru is undefined which should be conservatively correct.
I previously tried adding a policy operand to vmerge/vadc etc., but this ended up being a lot of churn.
This removes a bunch of redundant vmv.v.vs that I noticed with EVL tail folding on llvm-test-suite.
>From cc2226380bf9ab3aa5382aee4707aa037ce4d12c Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Wed, 30 Jul 2025 22:07:06 +0800
Subject: [PATCH 1/2] Precommit tests
---
llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll | 13 +++++++++++++
.../test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir | 17 +++++++++++++++++
2 files changed, 30 insertions(+)
diff --git a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll
index 1e2e7795f6546..b4c1c523aec56 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll
@@ -222,3 +222,16 @@ define <vscale x 1 x i64> @vleff_move_past_passthru(ptr %p, ptr %q, iXLen %avl)
%b = call <vscale x 1 x i64> @llvm.riscv.vmv.v.v.nxv1i64(<vscale x 1 x i64> %passthru, <vscale x 1 x i64> %vec, iXLen %avl)
ret <vscale x 1 x i64> %b
}
+
+define <vscale x 1 x i64> @vmerge(<vscale x 1 x i64> %passthru, <vscale x 1 x i64> %x, <vscale x 1 x i64> %y, <vscale x 1 x i1> %m, iXLen %avl) {
+; CHECK-LABEL: vmerge:
+; CHECK: # %bb.0:
+; CHECK-NEXT: vsetvli zero, a0, e64, m1, tu, ma
+; CHECK-NEXT: vmv1r.v v11, v8
+; CHECK-NEXT: vmerge.vvm v11, v9, v10, v0
+; CHECK-NEXT: vmv.v.v v8, v11
+; CHECK-NEXT: ret
+ %a = call <vscale x 1 x i64> @llvm.riscv.vmerge.nxv1i64.nxv1i64(<vscale x 1 x i64> %passthru, <vscale x 1 x i64> %x, <vscale x 1 x i64> %y, <vscale x 1 x i1> %m, iXLen %avl)
+ %b = call <vscale x 1 x i64> @llvm.riscv.vmv.v.v.nxv1i64(<vscale x 1 x i64> %passthru, <vscale x 1 x i64> %a, iXLen %avl)
+ ret <vscale x 1 x i64> %b
+}
diff --git a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir
index 6e106e50634f0..66c9268b51fe4 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir
+++ b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir
@@ -152,3 +152,20 @@ body: |
%y:gpr = ADDI $x0, 1
%z:vr = PseudoVMV_V_V_M1 %passthru, %x, 4, 5 /* e32 */, 0 /* tu, mu */
...
+---
+name: vmerge_vvm
+body: |
+ bb.0:
+ liveins: $v8, $v0
+ ; CHECK-LABEL: name: vmerge_vvm
+ ; CHECK: liveins: $v8, $v0
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: %passthru:vr = COPY $v8
+ ; CHECK-NEXT: %mask:vmv0 = COPY $v0
+ ; CHECK-NEXT: %x:vrnov0 = PseudoVMERGE_VVM_M1 $noreg, %passthru, $noreg, %mask, 4, 5 /* e32 */
+ ; CHECK-NEXT: %z:vr = PseudoVMV_V_V_M1 %passthru, %x, 4, 5 /* e32 */, 0 /* tu, mu */
+ %passthru:vr = COPY $v8
+ %mask:vmv0 = COPY $v0
+ %x:vrnov0 = PseudoVMERGE_VVM_M1 $noreg, %passthru, $noreg, %mask, 4, 5 /* e32 */
+ %z:vr = PseudoVMV_V_V_M1 %passthru, %x, 4, 5 /* e32 */, 0 /* tu, mu */
+...
>From e6e3f7747d78878c6a10d9e88d3a5f691054f5ce Mon Sep 17 00:00:00 2001
From: Luke Lau <luke at igalia.com>
Date: Wed, 30 Jul 2025 21:59:23 +0800
Subject: [PATCH 2/2] [RISCV] Fold vmv.v.v into vmerge
We support folding vmv.v.v into its source via the foldVMV_V_V peephole, but currently it requires that the source has a policy operand.
PseudoVMERGEs (as well as add-with-carry/subtract-with-borrow pseudos) don't have a policy operand, and instead just seem to derive TA/TU from whether or not the passthru is undef, since the mask policy doesn't affect them.
This patch allows pseudos without policy operands, given that if there's no policy operand then it will default to TU when the passthru is undefined which should be conservatively correct.
I previously tried adding a policy operand to vmerge/vadc etc., but this ended up being a lot of churn.
This removes a bunch of redundant vmv.v.vs that I noticed with EVL tail folding on llvm-test-suite.
---
llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp | 17 +++++++++--------
.../RISCV/rvv/fixed-vectors-insert-subvector.ll | 6 ++----
llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll | 4 +---
.../test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir | 5 ++---
4 files changed, 14 insertions(+), 18 deletions(-)
diff --git a/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp b/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
index c1cc19b503deb..050de3d58a2f2 100644
--- a/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
+++ b/llvm/lib/Target/RISCV/RISCVVectorPeephole.cpp
@@ -646,8 +646,7 @@ bool RISCVVectorPeephole::foldVMV_V_V(MachineInstr &MI) {
if (!Src || Src->hasUnmodeledSideEffects() ||
Src->getParent() != MI.getParent() ||
!RISCVII::isFirstDefTiedToFirstUse(Src->getDesc()) ||
- !RISCVII::hasVLOp(Src->getDesc().TSFlags) ||
- !RISCVII::hasVecPolicyOp(Src->getDesc().TSFlags))
+ !RISCVII::hasVLOp(Src->getDesc().TSFlags))
return false;
// Src's dest needs to have the same EEW as MI's input.
@@ -681,12 +680,14 @@ bool RISCVVectorPeephole::foldVMV_V_V(MachineInstr &MI) {
*Src->getParent()->getParent()));
}
- // If MI was tail agnostic and the VL didn't increase, preserve it.
- int64_t Policy = RISCVVType::TAIL_UNDISTURBED_MASK_UNDISTURBED;
- if ((MI.getOperand(5).getImm() & RISCVVType::TAIL_AGNOSTIC) &&
- RISCV::isVLKnownLE(MI.getOperand(3), SrcVL))
- Policy |= RISCVVType::TAIL_AGNOSTIC;
- Src->getOperand(RISCVII::getVecPolicyOpNum(Src->getDesc())).setImm(Policy);
+ if (RISCVII::hasVecPolicyOp(Src->getDesc().TSFlags)) {
+ // If MI was tail agnostic and the VL didn't increase, preserve it.
+ int64_t Policy = RISCVVType::TAIL_UNDISTURBED_MASK_UNDISTURBED;
+ if ((MI.getOperand(5).getImm() & RISCVVType::TAIL_AGNOSTIC) &&
+ RISCV::isVLKnownLE(MI.getOperand(3), SrcVL))
+ Policy |= RISCVVType::TAIL_AGNOSTIC;
+ Src->getOperand(RISCVII::getVecPolicyOpNum(Src->getDesc())).setImm(Policy);
+ }
MRI->constrainRegClass(Src->getOperand(0).getReg(),
MRI->getRegClass(MI.getOperand(0).getReg()));
diff --git a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
index 5747bbb3f100c..bd37443e89838 100644
--- a/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-insert-subvector.ll
@@ -554,9 +554,8 @@ define <vscale x 2 x i1> @insert_nxv2i1_v4i1_0(<vscale x 2 x i1> %v, ptr %svp) {
; VLA-NEXT: vsetivli zero, 4, e8, mf4, ta, ma
; VLA-NEXT: vmv.v.i v10, 0
; VLA-NEXT: vmv1r.v v0, v8
-; VLA-NEXT: vmerge.vim v8, v10, 1, v0
; VLA-NEXT: vsetvli zero, zero, e8, mf4, tu, ma
-; VLA-NEXT: vmv.v.v v9, v8
+; VLA-NEXT: vmerge.vim v9, v10, 1, v0
; VLA-NEXT: vsetvli a0, zero, e8, mf4, ta, ma
; VLA-NEXT: vmsne.vi v0, v9, 0
; VLA-NEXT: ret
@@ -568,9 +567,8 @@ define <vscale x 2 x i1> @insert_nxv2i1_v4i1_0(<vscale x 2 x i1> %v, ptr %svp) {
; VLS-NEXT: vmv.v.i v9, 0
; VLS-NEXT: vmerge.vim v10, v9, 1, v0
; VLS-NEXT: vmv1r.v v0, v8
-; VLS-NEXT: vmerge.vim v8, v9, 1, v0
; VLS-NEXT: vsetvli zero, zero, e8, mf4, tu, ma
-; VLS-NEXT: vmv.v.v v10, v8
+; VLS-NEXT: vmerge.vim v10, v9, 1, v0
; VLS-NEXT: vsetvli zero, zero, e8, mf4, ta, ma
; VLS-NEXT: vmsne.vi v0, v10, 0
; VLS-NEXT: ret
diff --git a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll
index b4c1c523aec56..2f2035b02b552 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.ll
@@ -227,9 +227,7 @@ define <vscale x 1 x i64> @vmerge(<vscale x 1 x i64> %passthru, <vscale x 1 x i6
; CHECK-LABEL: vmerge:
; CHECK: # %bb.0:
; CHECK-NEXT: vsetvli zero, a0, e64, m1, tu, ma
-; CHECK-NEXT: vmv1r.v v11, v8
-; CHECK-NEXT: vmerge.vvm v11, v9, v10, v0
-; CHECK-NEXT: vmv.v.v v8, v11
+; CHECK-NEXT: vmerge.vvm v8, v9, v10, v0
; CHECK-NEXT: ret
%a = call <vscale x 1 x i64> @llvm.riscv.vmerge.nxv1i64.nxv1i64(<vscale x 1 x i64> %passthru, <vscale x 1 x i64> %x, <vscale x 1 x i64> %y, <vscale x 1 x i1> %m, iXLen %avl)
%b = call <vscale x 1 x i64> @llvm.riscv.vmv.v.v.nxv1i64(<vscale x 1 x i64> %passthru, <vscale x 1 x i64> %a, iXLen %avl)
diff --git a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir
index 66c9268b51fe4..9c3e96d818556 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir
+++ b/llvm/test/CodeGen/RISCV/rvv/vmv.v.v-peephole.mir
@@ -160,10 +160,9 @@ body: |
; CHECK-LABEL: name: vmerge_vvm
; CHECK: liveins: $v8, $v0
; CHECK-NEXT: {{ $}}
- ; CHECK-NEXT: %passthru:vr = COPY $v8
+ ; CHECK-NEXT: %passthru:vrnov0 = COPY $v8
; CHECK-NEXT: %mask:vmv0 = COPY $v0
- ; CHECK-NEXT: %x:vrnov0 = PseudoVMERGE_VVM_M1 $noreg, %passthru, $noreg, %mask, 4, 5 /* e32 */
- ; CHECK-NEXT: %z:vr = PseudoVMV_V_V_M1 %passthru, %x, 4, 5 /* e32 */, 0 /* tu, mu */
+ ; CHECK-NEXT: %x:vrnov0 = PseudoVMERGE_VVM_M1 %passthru, %passthru, $noreg, %mask, 4, 5 /* e32 */
%passthru:vr = COPY $v8
%mask:vmv0 = COPY $v0
%x:vrnov0 = PseudoVMERGE_VVM_M1 $noreg, %passthru, $noreg, %mask, 4, 5 /* e32 */
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