[llvm] 71039bb - [AMDGPU] Fix register class constraints for si-fold-operands pass when folding immediate into copies (#131387)

[via llvm-commits]

Author: mssefat
Date: 2025-04-30T17:36:46-05:00
New Revision: 71039bbc581b59bdec25ed1e1d4cc6e772d5bb0c

URL: https://github.com/llvm/llvm-project/commit/71039bbc581b59bdec25ed1e1d4cc6e772d5bb0c
DIFF: https://github.com/llvm/llvm-project/commit/71039bbc581b59bdec25ed1e1d4cc6e772d5bb0c.diff

LOG: [AMDGPU] Fix register class constraints for si-fold-operands pass when folding immediate into copies (#131387)

Fixes https://github.com/llvm/llvm-project/issues/130020

This fixes an issue where the si-fold-operands pass would incorrectly
fold immediate values into COPY instructions targeting av_32 registers.

The pass now checks register class constraints before attempting to fold
the immediate.

Added: 
    

Modified: 
    llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
    llvm/test/CodeGen/AMDGPU/fold-imm-copy.mir

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
index 1547142a8d5c6..f1cbc26dcadf0 100644
--- a/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
+++ b/llvm/lib/Target/AMDGPU/SIFoldOperands.cpp
@@ -1067,6 +1067,16 @@ void SIFoldOperandsImpl::foldOperand(
     if (MovOp == AMDGPU::COPY)
       return;
 
+    // Fold if the destination register class of the MOV instruction (ResRC)
+    // is a superclass of (or equal to) the destination register class of the
+    // COPY (DestRC). If this condition fails, folding would be illegal.
+    const MCInstrDesc &MovDesc = TII->get(MovOp);
+    assert(MovDesc.getNumDefs() > 0 && MovDesc.operands()[0].RegClass != -1);
+    const TargetRegisterClass *ResRC =
+        TRI->getRegClass(MovDesc.operands()[0].RegClass);
+    if (!DestRC->hasSuperClassEq(ResRC))
+      return;
+
     MachineInstr::mop_iterator ImpOpI = UseMI->implicit_operands().begin();
     MachineInstr::mop_iterator ImpOpE = UseMI->implicit_operands().end();
     while (ImpOpI != ImpOpE) {

diff  --git a/llvm/test/CodeGen/AMDGPU/fold-imm-copy.mir b/llvm/test/CodeGen/AMDGPU/fold-imm-copy.mir
index 300bae7551ca5..706c0d8178d70 100644
--- a/llvm/test/CodeGen/AMDGPU/fold-imm-copy.mir
+++ b/llvm/test/CodeGen/AMDGPU/fold-imm-copy.mir
@@ -202,52 +202,70 @@ body:             |
 
 ...
 
-# FIXME: Register class restrictions of av register not respected,
-# issue 130020
-
-# ---
-# name: s_mov_b32_inlineimm_copy_s_to_av_32
-# tracksRegLiveness: true
-# body:             |
-#   bb.0:
-#     %0:sreg_32 = S_MOV_B32 32
-#     %1:av_32 = COPY %0
-#     $agpr0 = COPY %1
-#     S_ENDPGM 0
-
-# ...
-
-# ---
-# name: v_mov_b32_inlineimm_copy_v_to_av_32
-# tracksRegLiveness: true
-# body:             |
-#  bb.0:
-#    %0:vgpr_32 = V_MOV_B32_e32 32, implicit $exec
-#    %1:av_32 = COPY %0
-#    $agpr0 = COPY %1
-#    S_ENDPGM 0
-# ...
-
-# ---
-# name: s_mov_b32_imm_literal_copy_s_to_av_32
-# tracksRegLiveness: true
-# body:             |
-#   bb.0:
-#     %0:sreg_32 = S_MOV_B32 999
-#     %1:av_32 = COPY %0
-#     $agpr0 = COPY %1
-#     S_ENDPGM 0
-
-# ...
-
-# ---
-# name: v_mov_b32_imm_literal_copy_v_to_av_32
-# tracksRegLiveness: true
-# body:             |
-#   bb.0:
-#     %0:vgpr_32 = V_MOV_B32_e32 999, implicit $exec
-#     %1:av_32 = COPY %0
-#     $agpr0 = COPY %1
-#     S_ENDPGM 0
-
-# ...
+---
+name: s_mov_b32_inlineimm_copy_s_to_av_32
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    ; GCN-LABEL: name: s_mov_b32_inlineimm_copy_s_to_av_32
+    ; GCN: [[S_MOV_B32_:%[0-9]+]]:sreg_32 = S_MOV_B32 32
+    ; GCN-NEXT: [[COPY:%[0-9]+]]:av_32 = COPY [[S_MOV_B32_]]
+    ; GCN-NEXT: $agpr0 = COPY [[COPY]]
+    ; GCN-NEXT: S_ENDPGM 0
+    %0:sreg_32 = S_MOV_B32 32
+    %1:av_32 = COPY %0
+    $agpr0 = COPY %1
+    S_ENDPGM 0
+
+...
+
+---
+name: v_mov_b32_inlineimm_copy_v_to_av_32
+tracksRegLiveness: true
+body:             |
+ bb.0:
+    ; GCN-LABEL: name: v_mov_b32_inlineimm_copy_v_to_av_32
+    ; GCN: [[V_MOV_B32_e32_:%[0-9]+]]:vgpr_32 = V_MOV_B32_e32 32, implicit $exec
+    ; GCN-NEXT: [[COPY:%[0-9]+]]:av_32 = COPY [[V_MOV_B32_e32_]]
+    ; GCN-NEXT: $agpr0 = COPY [[COPY]]
+    ; GCN-NEXT: S_ENDPGM 0
+   %0:vgpr_32 = V_MOV_B32_e32 32, implicit $exec
+   %1:av_32 = COPY %0
+   $agpr0 = COPY %1
+   S_ENDPGM 0
+
+...
+
+---
+name: s_mov_b32_imm_literal_copy_s_to_av_32
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    ; GCN-LABEL: name: s_mov_b32_imm_literal_copy_s_to_av_32
+    ; GCN: [[S_MOV_B32_:%[0-9]+]]:sreg_32 = S_MOV_B32 999
+    ; GCN-NEXT: [[COPY:%[0-9]+]]:av_32 = COPY [[S_MOV_B32_]]
+    ; GCN-NEXT: $agpr0 = COPY [[COPY]]
+    ; GCN-NEXT: S_ENDPGM 0
+    %0:sreg_32 = S_MOV_B32 999
+    %1:av_32 = COPY %0
+    $agpr0 = COPY %1
+    S_ENDPGM 0
+
+...
+
+---
+name: v_mov_b32_imm_literal_copy_v_to_av_32
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    ; GCN-LABEL: name: v_mov_b32_imm_literal_copy_v_to_av_32
+    ; GCN: [[V_MOV_B32_e32_:%[0-9]+]]:vgpr_32 = V_MOV_B32_e32 999, implicit $exec
+    ; GCN-NEXT: [[COPY:%[0-9]+]]:av_32 = COPY [[V_MOV_B32_e32_]]
+    ; GCN-NEXT: $agpr0 = COPY [[COPY]]
+    ; GCN-NEXT: S_ENDPGM 0
+    %0:vgpr_32 = V_MOV_B32_e32 999, implicit $exec
+    %1:av_32 = COPY %0
+    $agpr0 = COPY %1
+    S_ENDPGM 0
+
+...