[AMDGPU][GFX908] IndirectCopyToAGPR: Confirm modified register is dst reg of accvgpr_write

IndirectCopyToAGPR should be reworked as to avoid optimizing during copy lowering. However, as it stands, the code is buggy. This patch replaces the call to definesRegister with modifiesRegister, and confirms that the dest reg of the found accvgpr_write is in fact the src reg of our copy.

Differential Revision: https://reviews.llvm.org/D149873

Change-Id: Id8a61659ac15565dcb970069d0624f0925a46e6d

Author: Jeffrey Byrnes

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -578,9 +578,12 @@ static void indirectCopyToAGPR(const SIInstrInfo &TII,
   if (!RegsOverlap) {
     for (auto Def = MI, E = MBB.begin(); Def != E; ) {
       --Def;
-      if (!Def->definesRegister(SrcReg, &RI))
+
+      if (!Def->modifiesRegister(SrcReg, &RI))
         continue;
-      if (Def->getOpcode() != AMDGPU::V_ACCVGPR_WRITE_B32_e64)
+
+      if (Def->getOpcode() != AMDGPU::V_ACCVGPR_WRITE_B32_e64 ||
+          Def->getOperand(0).getReg() != SrcReg)
         break;
 
       MachineOperand &DefOp = Def->getOperand(1);

llvm/test/CodeGen/AMDGPU/accvgpr-copy.mir

@@ -900,9 +900,11 @@ body:             |
     ; GFX908-NEXT: $vgpr1 = V_ACCVGPR_READ_B32_e64 $agpr1, implicit $exec, implicit $agpr0_agpr1
     ; GFX908-NEXT: $agpr2 = V_ACCVGPR_WRITE_B32_e64 $vgpr1, implicit $exec, implicit-def $agpr1_agpr2
     ; GFX908-NEXT: $vgpr0 = V_ACCVGPR_READ_B32_e64 $agpr0, implicit $exec, implicit $agpr0_agpr1
-    ; GFX908-NEXT: $agpr1 = V_ACCVGPR_WRITE_B32_e64 $vgpr0, implicit $exec, implicit $exec, implicit-def $agpr1_agpr2
-    ; GFX908-NEXT: $agpr4 = V_ACCVGPR_WRITE_B32_e64 $vgpr0, implicit $exec, implicit-def $agpr3_agpr4, implicit $agpr1_agpr2
-    ; GFX908-NEXT: $agpr3 = V_ACCVGPR_WRITE_B32_e64 $vgpr0, implicit $exec, implicit killed $agpr1_agpr2, implicit $exec
+    ; GFX908-NEXT: $agpr1 = V_ACCVGPR_WRITE_B32_e64 killed $vgpr0, implicit $exec, implicit $exec, implicit-def $agpr1_agpr2
+    ; GFX908-NEXT: $vgpr0 = V_ACCVGPR_READ_B32_e64 $agpr2, implicit $exec, implicit $agpr1_agpr2
+    ; GFX908-NEXT: $agpr4 = V_ACCVGPR_WRITE_B32_e64 killed $vgpr0, implicit $exec, implicit-def $agpr3_agpr4
+    ; GFX908-NEXT: $vgpr255 = V_ACCVGPR_READ_B32_e64 killed $agpr1, implicit $exec, implicit killed $agpr1_agpr2
+    ; GFX908-NEXT: $agpr3 = V_ACCVGPR_WRITE_B32_e64 killed $vgpr255, implicit $exec, implicit $exec
     ; GFX90A-LABEL: name: a2_to_a2_implicit_defs
     ; GFX90A: liveins: $agpr0_agpr1
     ; GFX90A-NEXT: {{  $}}