MC: Allow getMaxInstLength to depend on the subtarget

Keep it optional in cases this is ever needed in some global
context. Currently it's only used for getting an upper bound inline
asm code size.

For AMDGPU, gfx10 increases the maximum instruction size to
20-bytes. This avoids penalizing older subtargets when estimating code
size, and making some annoying branch relaxation test adjustments.

llvm-svn: 361405

1 files changed, 8 insertions, 4 deletions

diff --git a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
index ea01416cd15..7db736766d2 100644
--- a/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
+++ b/llvm/lib/Target/AMDGPU/Disassembler/AMDGPUDisassembler.cpp
@@ -28,6 +28,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCDisassembler/MCDisassembler.h"
 #include "llvm/MC/MCExpr.h"
@@ -56,6 +57,12 @@ using namespace llvm;
 
 using DecodeStatus = llvm::MCDisassembler::DecodeStatus;
 
+AMDGPUDisassembler::AMDGPUDisassembler(const MCSubtargetInfo &STI,
+                                       MCContext &Ctx,
+                                       MCInstrInfo const *MCII) :
+  MCDisassembler(STI, Ctx), MCII(MCII), MRI(*Ctx.getRegisterInfo()),
+  TargetMaxInstBytes(Ctx.getAsmInfo()->getMaxInstLength(&STI)) {}
+
 inline static MCDisassembler::DecodeStatus
 addOperand(MCInst &Inst, const MCOperand& Opnd) {
   Inst.addOperand(Opnd);
@@ -186,10 +193,7 @@ DecodeStatus AMDGPUDisassembler::getInstruction(MCInst &MI, uint64_t &Size,
   if (!STI.getFeatureBits()[AMDGPU::FeatureGCN3Encoding] && !isGFX10())
     report_fatal_error("Disassembly not yet supported for subtarget");
 
-  unsigned MaxInstBytesNum = (std::min)(
-    STI.getFeatureBits()[AMDGPU::FeatureGFX10] ? (size_t) 20 :
-    STI.getFeatureBits()[AMDGPU::FeatureVOP3Literal] ? (size_t) 12 : (size_t)8,
-    Bytes_.size());
+  unsigned MaxInstBytesNum = std::min((size_t)TargetMaxInstBytes, Bytes_.size());
   Bytes = Bytes_.slice(0, MaxInstBytesNum);
 
   DecodeStatus Res = MCDisassembler::Fail;