[llvm] da8f692 - AMDGPU: Handle V->A MFMA copy from case with immediate src2 (#153023)

[via llvm-commits]

Author: Matt Arsenault
Date: 2025-09-03T16:21:46+09:00
New Revision: da8f692e3e6ecc7f91e4d0ff945613cabc103c28

URL: https://github.com/llvm/llvm-project/commit/da8f692e3e6ecc7f91e4d0ff945613cabc103c28
DIFF: https://github.com/llvm/llvm-project/commit/da8f692e3e6ecc7f91e4d0ff945613cabc103c28.diff

LOG: AMDGPU: Handle V->A MFMA copy from case with immediate src2 (#153023)

Handle a special case for copies from AGPR VGPR on the MFMA inputs.
If the "input" is really a subregister def, we will not see the
usual copy to VGPR for src2, only the read of the subregister def.
Not sure if this pattern appears in practice.

Added: 
    

Modified: 
    llvm/lib/Target/AMDGPU/AMDGPURewriteAGPRCopyMFMA.cpp
    llvm/test/CodeGen/AMDGPU/rewrite-vgpr-mfma-to-agpr-copy-from.mir

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/AMDGPU/AMDGPURewriteAGPRCopyMFMA.cpp b/llvm/lib/Target/AMDGPU/AMDGPURewriteAGPRCopyMFMA.cpp
index 5468bdd81cd98..21cf9cc6878fb 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPURewriteAGPRCopyMFMA.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPURewriteAGPRCopyMFMA.cpp
@@ -375,8 +375,11 @@ bool AMDGPURewriteAGPRCopyMFMAImpl::tryFoldCopiesFromAGPR(
     Register CopyDstReg = UseMI.getOperand(0).getReg();
     if (!CopyDstReg.isVirtual())
       continue;
+    for (MachineOperand &CopyUseMO : MRI.reg_nodbg_operands(CopyDstReg)) {
+      if (!CopyUseMO.readsReg())
+        continue;
 
-    for (MachineInstr &CopyUseMI : MRI.use_instructions(CopyDstReg)) {
+      MachineInstr &CopyUseMI = *CopyUseMO.getParent();
       if (isRewriteCandidate(CopyUseMI)) {
         if (tryReassigningMFMAChain(CopyUseMI, CopyDstReg,
                                     VRM.getPhys(CopyDstReg)))

diff  --git a/llvm/test/CodeGen/AMDGPU/rewrite-vgpr-mfma-to-agpr-copy-from.mir b/llvm/test/CodeGen/AMDGPU/rewrite-vgpr-mfma-to-agpr-copy-from.mir
index e636f6e6c6ca7..ad490f8fe54d8 100644
--- a/llvm/test/CodeGen/AMDGPU/rewrite-vgpr-mfma-to-agpr-copy-from.mir
+++ b/llvm/test/CodeGen/AMDGPU/rewrite-vgpr-mfma-to-agpr-copy-from.mir
@@ -187,8 +187,8 @@ body:             |
     ; CHECK-NEXT: [[COPY1:%[0-9]+]]:av_64_align2 = COPY $vgpr0_vgpr1
     ; CHECK-NEXT: [[COPY2:%[0-9]+]]:av_64_align2 = COPY $vgpr2_vgpr3
     ; CHECK-NEXT: [[GLOBAL_LOAD_DWORDX4_:%[0-9]+]]:areg_128_align2 = GLOBAL_LOAD_DWORDX4 [[COPY]], 0, 0, implicit $exec :: (load (s128), addrspace 1)
-    ; CHECK-NEXT: [[COPY3:%[0-9]+]]:vreg_128_align2 = COPY [[GLOBAL_LOAD_DWORDX4_]]
-    ; CHECK-NEXT: [[COPY3:%[0-9]+]].sub0_sub1:vreg_128_align2 = V_MFMA_F64_4X4X4F64_vgprcd_e64 [[COPY1]], [[COPY2]], 0, 0, 0, 0, implicit $mode, implicit $exec
+    ; CHECK-NEXT: [[COPY3:%[0-9]+]]:areg_128_align2 = COPY [[GLOBAL_LOAD_DWORDX4_]]
+    ; CHECK-NEXT: [[COPY3:%[0-9]+]].sub0_sub1:areg_128_align2 = V_MFMA_F64_4X4X4F64_e64 [[COPY1]], [[COPY2]], 0, 0, 0, 0, implicit $mode, implicit $exec
     ; CHECK-NEXT: GLOBAL_STORE_DWORDX4 [[COPY]], [[COPY3]], 0, 0, implicit $exec :: (store (s128), addrspace 1)
     ; CHECK-NEXT: SI_RETURN
     %0:vreg_64_align2 = COPY $vgpr4_vgpr5