[llvm] [AMDGPU] Fix RewriteMFMAFormSchedStage (PR #194887)

via llvm-commits llvm-commits at lists.llvm.org
Wed Apr 29 08:33:00 PDT 2026


https://github.com/xgxanq created https://github.com/llvm/llvm-project/pull/194887

1.RegionIdx is a field from the base class GCNSchedStage that tracks the current scheduling region index during normal scheduling. But rewrite() runs as a pre-pass (called from initGCNSchedStage(), before any region scheduling loop。
2.need to pre-check the dst and src2 in initHeuristics;
3.If the reaching use of the dst is a sub-reg, non-MFMA, and in the same basic block as the dst, we should also avoid creating redundant virtual registers and copies.

I can't create branches directly from llvm-project. As for stacked PRs, I can't implement that for now. So I forked two separate branches in my forked repo, and linked them together in the PR description. You can refer to https://github.com/llvm/llvm-project/pull/193429 to understand the fix just through the changes of the unit tests.

>From 6e08dcf6e65aa01150bda153fc09dbfaecd2b89b Mon Sep 17 00:00:00 2001
From: anqfu <anqfu at amd.com>
Date: Wed, 29 Apr 2026 15:10:42 +0000
Subject: [PATCH] [AMDGPU] Fix RewriteMFMAFormSchedStage

---
 llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp   | 118 +++---
 llvm/lib/Target/AMDGPU/GCNSchedStrategy.h     |   8 +-
 .../rewrite-mfma-form-check-half-rewrite.mir  |  86 ++++
 .../rewrite-mfma-form-v7slice-pattern.ll      | 380 ++++++++++++++++++
 4 files changed, 543 insertions(+), 49 deletions(-)
 create mode 100644 llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-check-half-rewrite.mir
 create mode 100644 llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-v7slice-pattern.ll

diff --git a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
index af2b2188c3081..0cd44b4404550 100644
--- a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
+++ b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.cpp
@@ -2250,6 +2250,31 @@ void GCNSchedStage::modifyRegionSchedule(unsigned RegionIdx,
   DAG.Regions[RegionIdx].first = MIOrder.front();
 }
 
+void RewriteMFMAFormStage::resetRewriteCandsToVGPR(
+    ArrayRef<std::pair<MachineInstr *, unsigned>> RewriteCands) {
+  for (auto &[MI, OriginalOpcode] : RewriteCands) {
+    assert(TII->isMAI(*MI));
+    const TargetRegisterClass *ADefRC =
+        DAG.MRI.getRegClass(MI->getOperand(0).getReg());
+    const TargetRegisterClass *VDefRC = SRI->getEquivalentVGPRClass(ADefRC);
+    DAG.MRI.setRegClass(MI->getOperand(0).getReg(), VDefRC);
+    MI->setDesc(TII->get(OriginalOpcode));
+
+    MachineOperand *Src2 = TII->getNamedOperand(*MI, AMDGPU::OpName::src2);
+    if (!Src2->isReg())
+      continue;
+
+    // Have to get src types separately since subregs may cause C and D
+    // registers to be different types even though the actual operand is
+    // the same size.
+    const TargetRegisterClass *AUseRC =
+        DAG.MRI.getRegClass(Src2->getReg());
+    const TargetRegisterClass *VUseRC =
+        SRI->getEquivalentVGPRClass(AUseRC);
+    DAG.MRI.setRegClass(Src2->getReg(), VUseRC);
+  }
+}
+
 bool RewriteMFMAFormStage::isRewriteCandidate(MachineInstr *MI) const {
 
   if (!static_cast<const SIInstrInfo *>(DAG.TII)->isMAI(*MI))
@@ -2272,10 +2297,18 @@ bool RewriteMFMAFormStage::initHeuristics(
       int ReplacementOp = AMDGPU::getMFMASrcCVDstAGPROp(MI.getOpcode());
       assert(ReplacementOp != -1);
 
+      MachineOperand *Src2 = TII->getNamedOperand(MI, AMDGPU::OpName::src2);
+      MachineOperand &Dst = MI.getOperand(0);
+      assert(Src2);
+      // Pre-validate: both dst and src2 (if a register) must be virtual.
+      if (!Dst.getReg().isVirtual() ||
+          (Src2->isReg() && !Src2->getReg().isVirtual())) {
+        continue;
+      }
+
       RewriteCands.push_back({&MI, MI.getOpcode()});
       MI.setDesc(TII->get(ReplacementOp));
 
-      MachineOperand *Src2 = TII->getNamedOperand(MI, AMDGPU::OpName::src2);
       if (Src2->isReg()) {
         SmallVector<SlotIndex, 8> Src2ReachingDefs;
         findReachingDefs(*Src2, DAG.LIS, Src2ReachingDefs);
@@ -2289,7 +2322,6 @@ bool RewriteMFMAFormStage::initHeuristics(
         }
       }
 
-      MachineOperand &Dst = MI.getOperand(0);
       SmallVector<MachineOperand *, 8> DstReachingUses;
 
       findReachingUses(&MI, DAG.LIS, DstReachingUses);
@@ -2339,7 +2371,7 @@ bool RewriteMFMAFormStage::initHeuristics(
 }
 
 int64_t RewriteMFMAFormStage::getRewriteCost(
-    const std::vector<std::pair<MachineInstr *, unsigned>> &RewriteCands,
+    ArrayRef<std::pair<MachineInstr *, unsigned>> RewriteCands,
     const DenseMap<MachineBasicBlock *, std::set<Register>> &CopyForUse,
     const SmallPtrSetImpl<MachineInstr *> &CopyForDef) {
   MachineBlockFrequencyInfo *MBFI = DAG.MBFI;
@@ -2354,6 +2386,10 @@ int64_t RewriteMFMAFormStage::getRewriteCost(
   unsigned AGPRThreshold = MaxVectorRegs.second;
   unsigned CombinedThreshold = ST.getMaxNumVGPRs(MF);
 
+  // Reset the classes that were changed to AGPR for better RB analysis.
+  // We must do rewriting after copy-insertion, as some defs of the register
+  // may require VGPR.  Additionally, if we bail out and don't perform the
+  // rewrite then these need to be restored anyway.
   for (unsigned Region = 0; Region < DAG.Regions.size(); Region++) {
     if (!RegionsWithExcessArchVGPR[Region])
       continue;
@@ -2391,8 +2427,10 @@ int64_t RewriteMFMAFormStage::getRewriteCost(
       SpillCost *= (int64_t)RelativeFreq;
 
     // If we have increased spilling in any block, just bail.
-    if (SpillCost > 0)
+    if (SpillCost > 0) {
+      resetRewriteCandsToVGPR(RewriteCands);
       return SpillCost;
+    }
 
     if (SpillCost < BestSpillCost)
       BestSpillCost = SpillCost;
@@ -2429,36 +2467,13 @@ int64_t RewriteMFMAFormStage::getRewriteCost(
     }
   }
 
-  // Reset the classes that were changed to AGPR for better RB analysis.
-  // We must do rewriting after copy-insertion, as some defs of the register
-  // may require VGPR.  Additionally, if we bail out and don't perform the
-  // rewrite then these need to be restored anyway.
-  for (auto &[MI, OriginalOpcode] : RewriteCands) {
-    assert(TII->isMAI(*MI));
-    const TargetRegisterClass *ADefRC =
-        DAG.MRI.getRegClass(MI->getOperand(0).getReg());
-    const TargetRegisterClass *VDefRC = SRI->getEquivalentVGPRClass(ADefRC);
-    DAG.MRI.setRegClass(MI->getOperand(0).getReg(), VDefRC);
-    MI->setDesc(TII->get(OriginalOpcode));
-
-    MachineOperand *Src2 = TII->getNamedOperand(*MI, AMDGPU::OpName::src2);
-    assert(Src2);
-    if (!Src2->isReg())
-      continue;
-
-    // Have to get src types separately since subregs may cause C and D
-    // registers to be different types even though the actual operand is
-    // the same size.
-    const TargetRegisterClass *AUseRC = DAG.MRI.getRegClass(Src2->getReg());
-    const TargetRegisterClass *VUseRC = SRI->getEquivalentVGPRClass(AUseRC);
-    DAG.MRI.setRegClass(Src2->getReg(), VUseRC);
-  }
+  resetRewriteCandsToVGPR(RewriteCands);
 
   return Cost + CopyCost;
 }
 
 bool RewriteMFMAFormStage::rewrite(
-    const std::vector<std::pair<MachineInstr *, unsigned>> &RewriteCands) {
+    ArrayRef<std::pair<MachineInstr *, unsigned>> RewriteCands) {
   DenseMap<MachineInstr *, unsigned> FirstMIToRegion;
   DenseMap<MachineInstr *, unsigned> LastMIToRegion;
 
@@ -2534,9 +2549,6 @@ bool RewriteMFMAFormStage::rewrite(
     MachineOperand *Src2 = TII->getNamedOperand(*MI, AMDGPU::OpName::src2);
     if (Src2->isReg()) {
       Register Src2Reg = Src2->getReg();
-      if (!Src2Reg.isVirtual())
-        return false;
-
       Register MappedReg = Src2->getReg();
       SmallVector<SlotIndex, 8> Src2ReachingDefs;
       findReachingDefs(*Src2, DAG.LIS, Src2ReachingDefs);
@@ -2602,9 +2614,6 @@ bool RewriteMFMAFormStage::rewrite(
 
     MachineOperand *Dst = &MI->getOperand(0);
     Register DstReg = Dst->getReg();
-    if (!DstReg.isVirtual())
-      return false;
-
     Register MappedReg = DstReg;
     SmallVector<MachineOperand *, 8> DstReachingUses;
 
@@ -2675,6 +2684,14 @@ bool RewriteMFMAFormStage::rewrite(
     }
 
     DenseSet<MachineOperand *> &DstRegSet = ReplaceMap[DstReg];
+
+    // For same-block sub-register uses: all RUs that share the same DstReg
+    // and are in the same MBB as the MFMA can reuse a single COPY instead of
+    // inserting one COPY per use.  The COPY is placed immediately after the
+    // MFMA so it dominates every same-block use regardless of their order in
+    // DstReachingUseCopies.
+    Register SameBlockNewUseReg;
+
     for (MachineOperand *RU : DstReachingUseCopies) {
       MachineBasicBlock *RUBlock = RU->getParent()->getParent();
       // Just keep track of the reaching use of this register by block. After we
@@ -2684,22 +2701,29 @@ bool RewriteMFMAFormStage::rewrite(
         continue;
       }
 
-      // Special case, the use is in the same block as the MFMA. Insert the copy
-      // just before the use.
+      // Special case: the use is in the same block as the MFMA. Insert a single
+      // COPY immediately after the MFMA and reuse it for all same-block uses.
+      if (SameBlockNewUseReg.isValid()) {
+        // Reuse the COPY already inserted for this DstReg; no new instruction.
+        RU->setReg(SameBlockNewUseReg);
+        continue;
+      }
+
+      // First same-block use: create one COPY placed right after the MFMA so
+      // it dominates all subsequent same-block uses of DstReg.
       const TargetRegisterClass *DstRC = DAG.MRI.getRegClass(DstReg);
       const TargetRegisterClass *VGPRRC = SRI->getEquivalentVGPRClass(DstRC);
-      Register NewUseReg = DAG.MRI.createVirtualRegister(VGPRRC);
-      MachineInstr *UseInst = RU->getParent();
+      SameBlockNewUseReg = DAG.MRI.createVirtualRegister(VGPRRC);
       MachineInstrBuilder VGPRCopy =
-          BuildMI(*UseInst->getParent(), UseInst->getIterator(),
-                  UseInst->getDebugLoc(), TII->get(TargetOpcode::COPY))
-              .addDef(NewUseReg, {}, 0)
+          BuildMI(*MI->getParent(), std::next(MI->getIterator()),
+                  MI->getDebugLoc(), TII->get(TargetOpcode::COPY))
+              .addDef(SameBlockNewUseReg, {}, 0)
               .addUse(DstReg, {}, 0);
       DAG.LIS->InsertMachineInstrInMaps(*VGPRCopy);
       // Since we know this use has only one reaching def, we can replace the
       // use reg.
-      RU->setReg(NewUseReg);
-      // Track the copy source operand for r eplacement.
+      RU->setReg(SameBlockNewUseReg);
+      // Track the copy source operand for replacement.
       DstRegSet.insert(&VGPRCopy->getOperand(1));
     }
 
@@ -2793,10 +2817,10 @@ bool RewriteMFMAFormStage::rewrite(
   RegionPressureMap LiveInUpdater(&DAG, false);
   LiveInUpdater.buildLiveRegMap();
 
-  for (unsigned Region = 0; Region < DAG.Regions.size(); Region++)
+  for (unsigned Region = 0; Region < DAG.Regions.size(); Region++) {
     DAG.LiveIns[Region] = LiveInUpdater.getLiveRegsForRegionIdx(Region);
-
-  DAG.Pressure[RegionIdx] = DAG.getRealRegPressure(RegionIdx);
+    DAG.Pressure[Region] = DAG.getRealRegPressure(Region);
+  }
 
   return true;
 }
diff --git a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.h b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.h
index 2cc9e81a65191..684267d381478 100644
--- a/llvm/lib/Target/AMDGPU/GCNSchedStrategy.h
+++ b/llvm/lib/Target/AMDGPU/GCNSchedStrategy.h
@@ -459,13 +459,17 @@ class RewriteMFMAFormStage : public GCNSchedStage {
   /// in initHeuristics. Uses \p CopyForUse and \p CopyForDef to calculate copy
   /// costs, and \p RewriteCands to undo rewriting.
   int64_t getRewriteCost(
-      const std::vector<std::pair<MachineInstr *, unsigned>> &RewriteCands,
+      ArrayRef<std::pair<MachineInstr *, unsigned>> RewriteCands,
       const DenseMap<MachineBasicBlock *, std::set<Register>> &CopyForUse,
       const SmallPtrSetImpl<MachineInstr *> &CopyForDef);
 
   /// Do the final rewrite on \p RewriteCands and insert any needed copies.
   bool
-  rewrite(const std::vector<std::pair<MachineInstr *, unsigned>> &RewriteCands);
+  rewrite(ArrayRef<std::pair<MachineInstr *, unsigned>> RewriteCands);
+  /// Resets all rewrite candidates in \p Cands back to their original VGPR
+  /// opcodes and register classes.
+  void resetRewriteCandsToVGPR(
+      ArrayRef<std::pair<MachineInstr *, unsigned>> RewriteCands);
 
   /// \returns true if this MI is a rewrite candidate.
   bool isRewriteCandidate(MachineInstr *MI) const;
diff --git a/llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-check-half-rewrite.mir b/llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-check-half-rewrite.mir
new file mode 100644
index 0000000000000..d23ee6c7fec76
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-check-half-rewrite.mir
@@ -0,0 +1,86 @@
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx950 \
+# RUN:     -run-pass=machine-scheduler \
+# RUN:     -amdgpu-disable-rewrite-mfma-form-sched-stage=false \
+# RUN:     -o - %s | FileCheck %s
+#
+# Test: RewriteMFMAFormStage — physical register in MFMA src2 aborts rewrite cleanly.
+#
+# Root cause (GCNSchedStrategy.cpp):
+#   rewrite() processes RewriteCands in iteration order. For each MFMA:
+#     MI->setDesc(ReplacementOp);              // opcode mutated
+#     if (!Src2Reg.isVirtual()) return false;  // mid-loop bail-out on physreg
+#   Fix: check isVirtual() in isRewriteCandidate() before adding to RewriteCands,
+#   so rewrite() never sees a physreg src2. Both MFMAs stay in VGPR form.
+#
+# Trigger:
+#   MFMA_B uses $vgpr4_vgpr5_vgpr6_vgpr7 (physical VGPR) as src2.
+#   With fix: isRewriteCandidate() rejects MFMA_B -> rewrite() not called ->
+#   no crash, both MFMAs remain in vreg_128_align2 / vgprcd form.
+#
+# CHECK-LABEL: name: test_bug2_physreg_src2
+# CHECK:       bb.0:
+# MFMA_A: virtual src2 but rewrite aborted (MFMA_B not a candidate) -> vgprcd stays.
+# CHECK:         %res_a:vreg_128_align2 = {{.*}} V_MFMA_SCALE_F32_16X16X128_F8F6F4_f4_f4_vgprcd_e64
+# MFMA_B: physical src2 — skipped by isRewriteCandidate, stays in vgprcd form.
+# CHECK:         %res_b:vreg_128_align2 = {{.*}} V_MFMA_SCALE_F32_16X16X128_F8F6F4_f4_f4_vgprcd_e64
+
+--- |
+  define void @test_bug2_physreg_src2() #0 {
+  entry:
+    unreachable
+  }
+
+  attributes #0 = { "amdgpu-waves-per-eu"="1,1" "amdgpu-flat-work-group-size"="64,64" }
+...
+
+---
+name:            test_bug2_physreg_src2
+tracksRegLiveness: true
+liveins:
+  - { reg: '$vgpr4' }
+  - { reg: '$vgpr5' }
+  - { reg: '$vgpr6' }
+  - { reg: '$vgpr7' }
+machineFunctionInfo:
+  isEntryFunction: true
+  scratchRSrcReg:  '$sgpr96_sgpr97_sgpr98_sgpr99'
+  stackPtrOffsetReg: '$sgpr32'
+  argumentInfo:
+    privateSegmentBuffer: { reg: '$sgpr0_sgpr1_sgpr2_sgpr3' }
+    kernargSegmentPtr:    { reg: '$sgpr4_sgpr5' }
+    workGroupIDX:         { reg: '$sgpr6' }
+    privateSegmentWaveByteOffset: { reg: '$sgpr7' }
+    workItemIDX:          { reg: '$vgpr0' }
+  sgprForEXECCopy: '$sgpr100_sgpr101'
+body: |
+  bb.0:
+    liveins: $vgpr0, $sgpr4_sgpr5, $vgpr4, $vgpr5, $vgpr6, $vgpr7
+
+    ; 9 x vreg_1024 = 288 VGPRs > 256: triggers RegionsWithExcessArchVGPR.
+    %0:vreg_1024 = IMPLICIT_DEF
+    %1:vreg_1024 = IMPLICIT_DEF
+    %2:vreg_1024 = IMPLICIT_DEF
+    %3:vreg_1024 = IMPLICIT_DEF
+    %4:vreg_1024 = IMPLICIT_DEF
+    %5:vreg_1024 = IMPLICIT_DEF
+    %6:vreg_1024 = IMPLICIT_DEF
+    %7:vreg_1024 = IMPLICIT_DEF
+    %8:vreg_1024 = IMPLICIT_DEF
+
+    %10:av_128_align2  = IMPLICIT_DEF
+    %11:av_128_align2  = IMPLICIT_DEF
+    %12:vreg_64_align2 = IMPLICIT_DEF
+    %13:vgpr_32        = IMPLICIT_DEF
+
+    SCHED_BARRIER 0
+
+    ; MFMA_A: all virtual registers.
+    %acc_a:vreg_128_align2 = IMPLICIT_DEF
+    %res_a:vreg_128_align2 = contract nofpexcept V_MFMA_SCALE_F32_16X16X128_F8F6F4_f4_f4_vgprcd_e64 %10:av_128_align2, %11:av_128_align2, %acc_a:vreg_128_align2, 4, 4, %12.sub0:vreg_64_align2, %13:vgpr_32, 0, 0, implicit $mode, implicit $exec
+
+    ; MFMA_B: src2 = $vgpr4_vgpr5_vgpr6_vgpr7 (physical VGPR) — triggers crash.
+    %res_b:vreg_128_align2 = contract nofpexcept V_MFMA_SCALE_F32_16X16X128_F8F6F4_f4_f4_vgprcd_e64 %10:av_128_align2, %11:av_128_align2, $vgpr4_vgpr5_vgpr6_vgpr7, 4, 4, %12.sub0:vreg_64_align2, %13:vgpr_32, 0, 0, implicit $mode, implicit $exec
+
+    KILL %0, %1, %2, %3, %4, %5, %6, %7, %8, %res_a, %res_b
+
+    S_ENDPGM 0
diff --git a/llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-v7slice-pattern.ll b/llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-v7slice-pattern.ll
new file mode 100644
index 0000000000000..7804a2f61c4c9
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/rewrite-mfma-form-v7slice-pattern.ll
@@ -0,0 +1,380 @@
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx950 \
+; RUN:     -amdgpu-disable-rewrite-mfma-form-sched-stage=false \
+; RUN:     < %s | FileCheck %s
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx950 \
+; RUN:     -amdgpu-disable-rewrite-mfma-form-sched-stage=false \
+; RUN:     -stop-before=machine-scheduler \
+; RUN:     < %s | FileCheck %s --check-prefix=BEFORE
+; RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx950 \
+; RUN:     -amdgpu-disable-rewrite-mfma-form-sched-stage=false \
+; RUN:     -stop-after=machine-scheduler \
+; RUN:     < %s | FileCheck %s --check-prefix=AFTER
+;
+; Test: RewriteMFMAFormStage — v7_slice pattern (gfx950, mfma.f32.16x16x32.f16)
+;
+; Distilled from v7_slice.llir (Triton matmul kernel, gfx950).
+;
+; Key structural features preserved from v7_slice:
+;   (1) Loop body (%loop) accumulates via loop-carried SCALAR float phis,
+;       NOT <4 x float> phis. Each MFMA acc is built by insertelement from
+;       4 individual float phis then used as src2/dst in MFMAs within the loop.
+;   (2) Epilogue (%epilogue) ALSO contains MFMAs: the final K-tile iteration
+;       is peeled. Epilogue MFMAs take scalar float phis from %loop as acc,
+;       then produce results consumed by fptrunc+store — Case 2.
+;   (3) Scalar float phis initialized to 0.0 in entry (non-MAI def) — Case 3.
+;
+; CFG: entry -> loop (back-edge) -> epilogue -> ret
+;
+; Pressure design (gfx950, 256 ArchVGPR limit):
+;   64 loop-carried scalar float phis = 64 VGPRs (non-MFMA pressure carriers).
+;   4 MFMA chains of 2, each acc = 4 float phis = 16 VGPRs in loop.
+;   Plus <8 x half> src0/src1 operands reused across chains = 8 VGPRs.
+;   Total in loop body: 64 + 16 + 8 = 88 VGPRs (not enough alone).
+;   Add 6 more <32 x float> loop-carried vec carriers = 192 VGPRs.
+;   Peak ArchVGPR = 192 + 64 + 16 + 8 = 280 > 256 -> RegionsWithExcessArchVGPR.
+;   After rewrite: scalar phis=64 VGPR, vec carriers=192 VGPR, MFMA acc->AGPR.
+;   getRewriteCost() < 0 -> rewrite() fires.
+;
+; Expected:
+;   Case 3: v_accvgpr_write inserted after insertelement defs of MFMA acc
+;           (entry zeroinitializer -> scalar float phi -> insertelement = non-MAI)
+;   Case 2: v_accvgpr_read before fptrunc in epilogue block
+;   MFMA opcodes: v_mfma_f32_16x16x32_f16 vgprcd -> agprcd form
+
+declare <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half>, <8 x half>, <4 x float>, i32 immarg, i32 immarg, i32 immarg)
+
+define amdgpu_kernel void @test_v7slice_scalar_phi_acc(
+; CHECK-LABEL: test_v7slice_scalar_phi_acc:
+; CHECK:       ; @test_v7slice_scalar_phi_acc
+; Case 3: v_accvgpr_write inserted for scalar-phi acc (non-MAI def -> AGPR init).
+; Loop body MFMAs use AGPR C/D (a[...], a[...], a[...], a[...]).
+; CHECK:       ; %bb.0:                                ; %entry
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, v{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:         v_accvgpr_write_b32 a{{[0-9]+}}, s{{[0-9]+}}
+; CHECK:       .LBB0_1:                                ; %loop
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; Case 2: epilogue MFMAs take VGPR src0/src1, AGPR C/D. v_accvgpr_read before fptrunc.
+; CHECK:       ; %bb.2:                                ; %epilogue
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_mfma_f32_16x16x32_f16 a[{{[0-9:]+}}], v[{{[0-9:]+}}], v[{{[0-9:]+}}], a[{{[0-9:]+}}]
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+; CHECK:         v_accvgpr_read_b32 v{{[0-9]+}}, a{{[0-9]+}}
+    ptr addrspace(1) %out,
+    <8 x half> %a0,
+    <8 x half> %a1,
+    <8 x half> %b0,
+    <8 x half> %b1,
+    i32 %n) #0 {
+entry:
+  br label %loop
+
+loop:
+  %i = phi i32 [ 0, %entry ], [ %i.next, %loop ]
+
+  ; -------------------------------------------------------------------
+  ; 8 x <32 x float> loop-carried vector carriers = 256 VGPRs.
+  ; Self-insert with variable index prevents folding.
+  ; Kept live by store use in loop body.
+  ; -------------------------------------------------------------------
+  %vc0 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc0n, %loop ]
+  %vc1 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc1n, %loop ]
+  %vc2 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc2n, %loop ]
+  %vc3 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc3n, %loop ]
+  %vc4 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc4n, %loop ]
+  %vc5 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc5n, %loop ]
+  %vc6 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc6n, %loop ]
+  %vc7 = phi <32 x float> [ zeroinitializer, %entry ], [ %vc7n, %loop ]
+
+  ; -------------------------------------------------------------------
+  ; 16 loop-carried scalar float phis = 16 VGPRs.
+  ; These are the per-element accumulator slots, mirroring v7_slice's
+  ; pattern where each output element is a separate loop-carried float.
+  ; Initialized to 0.0 in entry (non-MAI def) -> Case 3 triggers on the
+  ; insertelement that builds the MFMA src2 from these scalars.
+  ; -------------------------------------------------------------------
+  ; MFMA chain A acc (4 floats):
+  %a0_0 = phi float [ 0.0, %entry ], [ %ra0_0, %loop ]
+  %a0_1 = phi float [ 0.0, %entry ], [ %ra0_1, %loop ]
+  %a0_2 = phi float [ 0.0, %entry ], [ %ra0_2, %loop ]
+  %a0_3 = phi float [ 0.0, %entry ], [ %ra0_3, %loop ]
+  ; MFMA chain B acc (4 floats):
+  %a1_0 = phi float [ 0.0, %entry ], [ %ra1_0, %loop ]
+  %a1_1 = phi float [ 0.0, %entry ], [ %ra1_1, %loop ]
+  %a1_2 = phi float [ 0.0, %entry ], [ %ra1_2, %loop ]
+  %a1_3 = phi float [ 0.0, %entry ], [ %ra1_3, %loop ]
+  ; MFMA chain C acc (4 floats):
+  %a2_0 = phi float [ 0.0, %entry ], [ %ra2_0, %loop ]
+  %a2_1 = phi float [ 0.0, %entry ], [ %ra2_1, %loop ]
+  %a2_2 = phi float [ 0.0, %entry ], [ %ra2_2, %loop ]
+  %a2_3 = phi float [ 0.0, %entry ], [ %ra2_3, %loop ]
+  ; MFMA chain D acc (4 floats):
+  %a3_0 = phi float [ 0.0, %entry ], [ %ra3_0, %loop ]
+  %a3_1 = phi float [ 0.0, %entry ], [ %ra3_1, %loop ]
+  %a3_2 = phi float [ 0.0, %entry ], [ %ra3_2, %loop ]
+  %a3_3 = phi float [ 0.0, %entry ], [ %ra3_3, %loop ]
+
+  ; -------------------------------------------------------------------
+  ; Build <4 x float> acc vectors from scalar phi elements (v7_slice pattern).
+  ; Each insertelement is a non-MAI def of an element of the acc register.
+  ; -------------------------------------------------------------------
+  %accA0 = insertelement <4 x float> poison,  float %a0_0, i32 0
+  %accA1 = insertelement <4 x float> %accA0, float %a0_1, i32 1
+  %accA2 = insertelement <4 x float> %accA1, float %a0_2, i32 2
+  %accA  = insertelement <4 x float> %accA2, float %a0_3, i32 3
+
+  %accB0 = insertelement <4 x float> poison,  float %a1_0, i32 0
+  %accB1 = insertelement <4 x float> %accB0, float %a1_1, i32 1
+  %accB2 = insertelement <4 x float> %accB1, float %a1_2, i32 2
+  %accB  = insertelement <4 x float> %accB2, float %a1_3, i32 3
+
+  %accC0 = insertelement <4 x float> poison,  float %a2_0, i32 0
+  %accC1 = insertelement <4 x float> %accC0, float %a2_1, i32 1
+  %accC2 = insertelement <4 x float> %accC1, float %a2_2, i32 2
+  %accC  = insertelement <4 x float> %accC2, float %a2_3, i32 3
+
+  %accD0 = insertelement <4 x float> poison,  float %a3_0, i32 0
+  %accD1 = insertelement <4 x float> %accD0, float %a3_1, i32 1
+  %accD2 = insertelement <4 x float> %accD1, float %a3_2, i32 2
+  %accD  = insertelement <4 x float> %accD2, float %a3_3, i32 3
+
+  ; -------------------------------------------------------------------
+  ; MFMA chains in loop body (2 MFMAs per chain, chained acc).
+  ; Results are loop-carried back via extractelement -> scalar phi.
+  ; -------------------------------------------------------------------
+  %rA_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %accA, i32 0, i32 0, i32 0)
+  %rA   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %rA_v, i32 0, i32 0, i32 0)
+
+  %rB_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %accB, i32 0, i32 0, i32 0)
+  %rB   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %rB_v, i32 0, i32 0, i32 0)
+
+  %rC_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %accC, i32 0, i32 0, i32 0)
+  %rC   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %rC_v, i32 0, i32 0, i32 0)
+
+  %rD_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %accD, i32 0, i32 0, i32 0)
+  %rD   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %rD_v, i32 0, i32 0, i32 0)
+
+  ; Extract scalar results to carry back via phi.
+  %ra0_0 = extractelement <4 x float> %rA, i32 0
+  %ra0_1 = extractelement <4 x float> %rA, i32 1
+  %ra0_2 = extractelement <4 x float> %rA, i32 2
+  %ra0_3 = extractelement <4 x float> %rA, i32 3
+
+  %ra1_0 = extractelement <4 x float> %rB, i32 0
+  %ra1_1 = extractelement <4 x float> %rB, i32 1
+  %ra1_2 = extractelement <4 x float> %rB, i32 2
+  %ra1_3 = extractelement <4 x float> %rB, i32 3
+
+  %ra2_0 = extractelement <4 x float> %rC, i32 0
+  %ra2_1 = extractelement <4 x float> %rC, i32 1
+  %ra2_2 = extractelement <4 x float> %rC, i32 2
+  %ra2_3 = extractelement <4 x float> %rC, i32 3
+
+  %ra3_0 = extractelement <4 x float> %rD, i32 0
+  %ra3_1 = extractelement <4 x float> %rD, i32 1
+  %ra3_2 = extractelement <4 x float> %rD, i32 2
+  %ra3_3 = extractelement <4 x float> %rD, i32 3
+
+  ; Vector carrier self-inserts (prevent register reuse).
+  %eidx = and i32 %i, 31
+  %vc0e = extractelement <32 x float> %vc0, i32 0
+  %vc1e = extractelement <32 x float> %vc1, i32 0
+  %vc2e = extractelement <32 x float> %vc2, i32 0
+  %vc3e = extractelement <32 x float> %vc3, i32 0
+  %vc4e = extractelement <32 x float> %vc4, i32 0
+  %vc5e = extractelement <32 x float> %vc5, i32 0
+  %vc6e = extractelement <32 x float> %vc6, i32 0
+  %vc7e = extractelement <32 x float> %vc7, i32 0
+  %vc0n = insertelement <32 x float> %vc0, float %vc0e, i32 %eidx
+  %vc1n = insertelement <32 x float> %vc1, float %vc1e, i32 %eidx
+  %vc2n = insertelement <32 x float> %vc2, float %vc2e, i32 %eidx
+  %vc3n = insertelement <32 x float> %vc3, float %vc3e, i32 %eidx
+  %vc4n = insertelement <32 x float> %vc4, float %vc4e, i32 %eidx
+  %vc5n = insertelement <32 x float> %vc5, float %vc5e, i32 %eidx
+  %vc6n = insertelement <32 x float> %vc6, float %vc6e, i32 %eidx
+  %vc7n = insertelement <32 x float> %vc7, float %vc7e, i32 %eidx
+
+  %vcs = fadd float %vc0e, %vc1e
+  store float %vcs, ptr addrspace(1) %out, align 4
+
+  %i.next = add i32 %i, 1
+  %cond = icmp eq i32 %i.next, %n
+  br i1 %cond, label %epilogue, label %loop
+
+epilogue:
+  ; -------------------------------------------------------------------
+  ; v7_slice pattern: epilogue ALSO has MFMAs (peeled final K-tile).
+  ; Acc built from the same scalar float phis coming out of %loop.
+  ; These insertelements are non-MAI defs -> Case 3.
+  ; -------------------------------------------------------------------
+  %eaccA0 = insertelement <4 x float> poison,   float %ra0_0, i32 0
+  %eaccA1 = insertelement <4 x float> %eaccA0, float %ra0_1, i32 1
+  %eaccA2 = insertelement <4 x float> %eaccA1, float %ra0_2, i32 2
+  %eaccA  = insertelement <4 x float> %eaccA2, float %ra0_3, i32 3
+
+  %eaccB0 = insertelement <4 x float> poison,   float %ra1_0, i32 0
+  %eaccB1 = insertelement <4 x float> %eaccB0, float %ra1_1, i32 1
+  %eaccB2 = insertelement <4 x float> %eaccB1, float %ra1_2, i32 2
+  %eaccB  = insertelement <4 x float> %eaccB2, float %ra1_3, i32 3
+
+  %eaccC0 = insertelement <4 x float> poison,   float %ra2_0, i32 0
+  %eaccC1 = insertelement <4 x float> %eaccC0, float %ra2_1, i32 1
+  %eaccC2 = insertelement <4 x float> %eaccC1, float %ra2_2, i32 2
+  %eaccC  = insertelement <4 x float> %eaccC2, float %ra2_3, i32 3
+
+  %eaccD0 = insertelement <4 x float> poison,   float %ra3_0, i32 0
+  %eaccD1 = insertelement <4 x float> %eaccD0, float %ra3_1, i32 1
+  %eaccD2 = insertelement <4 x float> %eaccD1, float %ra3_2, i32 2
+  %eaccD  = insertelement <4 x float> %eaccD2, float %ra3_3, i32 3
+
+  ; Epilogue MFMAs (2 per chain, as in v7_slice).
+  %erA_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %eaccA, i32 0, i32 0, i32 0)
+  %erA   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %erA_v, i32 0, i32 0, i32 0)
+
+  %erB_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %eaccB, i32 0, i32 0, i32 0)
+  %erB   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %erB_v, i32 0, i32 0, i32 0)
+
+  %erC_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %eaccC, i32 0, i32 0, i32 0)
+  %erC   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %erC_v, i32 0, i32 0, i32 0)
+
+  %erD_v = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a0, <8 x half> %b0, <4 x float> %eaccD, i32 0, i32 0, i32 0)
+  %erD   = call <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half> %a1, <8 x half> %b1, <4 x float> %erD_v, i32 0, i32 0, i32 0)
+
+  ; -------------------------------------------------------------------
+  ; Non-MAI use of epilogue MFMA results via fptrunc (Case 2).
+  ; v7_slice: results shuffled and fptrunc'd to fp16 for stores.
+  ; -------------------------------------------------------------------
+  %shA = shufflevector <4 x float> %erA, <4 x float> poison, <2 x i32> <i32 0, i32 1>
+  %hA  = fptrunc <2 x float> %shA to <2 x half>
+  store <2 x half> %hA, ptr addrspace(1) %out, align 2
+
+  %shB = shufflevector <4 x float> %erB, <4 x float> poison, <2 x i32> <i32 0, i32 1>
+  %hB  = fptrunc <2 x float> %shB to <2 x half>
+  %pB  = getelementptr i16, ptr addrspace(1) %out, i32 2
+  store <2 x half> %hB, ptr addrspace(1) %pB, align 2
+
+  %shC = shufflevector <4 x float> %erC, <4 x float> poison, <2 x i32> <i32 0, i32 1>
+  %hC  = fptrunc <2 x float> %shC to <2 x half>
+  %pC  = getelementptr i16, ptr addrspace(1) %out, i32 4
+  store <2 x half> %hC, ptr addrspace(1) %pC, align 2
+
+  %shD = shufflevector <4 x float> %erD, <4 x float> poison, <2 x i32> <i32 0, i32 1>
+  %hD  = fptrunc <2 x float> %shD to <2 x half>
+  %pD  = getelementptr i16, ptr addrspace(1) %out, i32 6
+  store <2 x half> %hD, ptr addrspace(1) %pD, align 2
+
+  ret void
+}
+
+attributes #0 = { "amdgpu-waves-per-eu"="1,1" "amdgpu-flat-work-group-size"="64,64" }
+
+; stop-before=machine-scheduler: MFMAs still in VGPR (vgprcd) form.
+; BEFORE-LABEL: name: test_v7slice_scalar_phi_acc
+; 8x V_MFMA_F32_16X16X32_F16_vgprcd_e64: VGPR form, rewrite not yet applied.
+; BEFORE:       bb.1.loop:
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; 8x V_MFMA_F32_16X16X32_F16_vgprcd_e64: epilogue peeled K-tile, VGPR form.
+; BEFORE:       bb.2.epilogue:
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; BEFORE:         %{{[0-9]+}}:vreg_128_align2 = V_MFMA_F32_16X16X32_F16_vgprcd_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+
+; AFTER-LABEL: name: test_v7slice_scalar_phi_acc
+; Case 3: 4x areg_128_align2 = COPY vreg (VGPR->AGPR init for scalar-phi acc).
+; AFTER:       bb.0.entry:
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = COPY %{{[0-9]+}}
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = COPY %{{[0-9]+}}
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = COPY %{{[0-9]+}}
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = COPY %{{[0-9]+}}
+; 8x V_MFMA_F32_16X16X32_F16_e64: AGPR form, loop-carried acc in areg.
+; AFTER:       bb.1.loop:
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; Case 2: vreg_128_align2 = COPY areg interleaved with epilogue MFMAs (AGPR->VGPR).
+; AFTER:       bb.2.epilogue:
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:vreg_128_align2 = COPY %{{[0-9]+}}
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:vreg_128_align2 = COPY %{{[0-9]+}}
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:vreg_128_align2 = COPY %{{[0-9]+}}
+; AFTER:         %{{[0-9]+}}:areg_128_align2 = V_MFMA_F32_16X16X32_F16_e64 %{{[0-9]+}}, %{{[0-9]+}}, %{{[0-9]+}}, 0, 0, 0, implicit $mode, implicit $exec
+; AFTER:         %{{[0-9]+}}:vreg_128_align2 = COPY %{{[0-9]+}}



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