AMDGPU: Move default wavesize hack for disassembler (#117422)

You cannot adjust the disassembler's subtarget. llvm-mc passes
the originally constructed MCSubtargetInfo around, rather than
querying the pointer in the disassembler instance.

Author: arsenm

llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp

@@ -45,26 +45,10 @@ using namespace llvm;
 
 using DecodeStatus = llvm::MCDisassembler::DecodeStatus;
 
-static const MCSubtargetInfo &addDefaultWaveSize(const MCSubtargetInfo &STI,
-                                                 MCContext &Ctx) {
-  if (!STI.hasFeature(AMDGPU::FeatureWavefrontSize64) &&
-      !STI.hasFeature(AMDGPU::FeatureWavefrontSize32)) {
-    MCSubtargetInfo &STICopy = Ctx.getSubtargetCopy(STI);
-    // If there is no default wave size it must be a generation before gfx10,
-    // these have FeatureWavefrontSize64 in their definition already. For gfx10+
-    // set wave32 as a default.
-    STICopy.ToggleFeature(AMDGPU::FeatureWavefrontSize32);
-    return STICopy;
-  }
-
-  return STI;
-}
-
 AMDGPUDisassembler::AMDGPUDisassembler(const MCSubtargetInfo &STI,
                                        MCContext &Ctx, MCInstrInfo const *MCII)
-    : MCDisassembler(addDefaultWaveSize(STI, Ctx), Ctx), MCII(MCII),
-      MRI(*Ctx.getRegisterInfo()), MAI(*Ctx.getAsmInfo()),
-      TargetMaxInstBytes(MAI.getMaxInstLength(&STI)),
+    : MCDisassembler(STI, Ctx), MCII(MCII), MRI(*Ctx.getRegisterInfo()),
+      MAI(*Ctx.getAsmInfo()), TargetMaxInstBytes(MAI.getMaxInstLength(&STI)),
       CodeObjectVersion(AMDGPU::getDefaultAMDHSACodeObjectVersion()) {
   // ToDo: AMDGPUDisassembler supports only VI ISA.
   if (!STI.hasFeature(AMDGPU::FeatureGCN3Encoding) && !isGFX10Plus())

llvm/lib/Target/AMDGPU/MCTargetDesc/AMDGPUMCTargetDesc.cpp

@@ -77,7 +77,22 @@ static MCSubtargetInfo *
 createAMDGPUMCSubtargetInfo(const Triple &TT, StringRef CPU, StringRef FS) {
   if (TT.getArch() == Triple::r600)
     return createR600MCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FS);
-  return createAMDGPUMCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FS);
+
+  MCSubtargetInfo *STI =
+      createAMDGPUMCSubtargetInfoImpl(TT, CPU, /*TuneCPU*/ CPU, FS);
+
+  // FIXME: We should error for the default target.
+  if (!STI->hasFeature(AMDGPU::FeatureWavefrontSize64) &&
+      !STI->hasFeature(AMDGPU::FeatureWavefrontSize32)) {
+    // If there is no default wave size it must be a generation before gfx10,
+    // these have FeatureWavefrontSize64 in their definition already. For gfx10+
+    // set wave32 as a default.
+    STI->ToggleFeature(AMDGPU::isGFX10Plus(*STI)
+                           ? AMDGPU::FeatureWavefrontSize32
+                           : AMDGPU::FeatureWavefrontSize64);
+  }
+
+  return STI;
 }
 
 static MCInstPrinter *createAMDGPUMCInstPrinter(const Triple &T,

llvm/test/MC/AMDGPU/unknown-target-cpu.s

@@ -1,4 +1,5 @@
-// RUN: llvm-mc -triple=amdgcn -show-encoding < %s | FileCheck %s
+// RUN: not llvm-mc -triple=amdgcn -show-encoding < %s | FileCheck %s
+// RUN: not llvm-mc -triple=amdgcn -show-encoding -filetype=null %s 2>&1 | FileCheck -check-prefix=ERR %s
 // RUN: llvm-mc -triple=amdgcn -mcpu=tahiti -show-encoding < %s | FileCheck %s
 
 // CHECK: v_cmp_lt_f32_e32 vcc, s2, v4            ; encoding: [0x02,0x08,0x02,0x7c]
@@ -7,7 +8,7 @@ v_cmp_lt_f32 vcc, s2, v4
 // CHECK: v_cndmask_b32_e32 v1, v2, v3, vcc       ; encoding: [0x02,0x07,0x02,0x00]
 v_cndmask_b32 v1, v2, v3, vcc
 
-// CHECK: v_mac_legacy_f32_e64 v1, v3, s5         ; encoding: [0x01,0x00,0x0c,0xd2,0x03,0x0b,0x00,0x00]
+// ERR: [[@LINE+1]]:1: error: instruction not supported on this GPU
 v_mac_legacy_f32 v1, v3, s5
 
 // CHECK: v_lshr_b32_e32 v0, v1, v2               ; encoding: [0x01,0x05,0x00,0x2a]