AMDGPU : Recalculate SGPRs when trap handler is supported

[wdng]

Ping.

[tony-tye]

lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp

215–222

Should check if MinNumSGPRs is less than TRAP_NUM_SGPRS, and perform the rounding after the subtraction? If so then replace with:

unsigned MinNumSGPRs = getTotalNumSGPRs(Features) / (WavesPerEU + 1);
if (Features.test(FeatureTrapHandler))
  MinNumSGPRs -= std::min(MinNumSGPRs, TRAP_NUM_SGPRS);
MinNumSGPRs = alignDown(MinNumSGPRs, getSGPRAllocGranule(Features)) + 1;
return std::min(MinNumSGPRs, getAddressableNumSGPRs(Features));

228–237

Should check if MaxNumSGPRs is less than TRAP_NUM_SGPRS? If so then replace with:

IsaVersion Version = getIsaVersion(Features);
unsigned AddressableNumSGPRs = getAddressableNumSGPRs(Features);
if (Version.Major >= 8 && !Addressable)
  AddressableNumSGPRs = 112;
unsigned MaxNumSGPRs = getTotalNumSGPRs(Features) / WavesPerEU;
if (Features.test(FeatureTrapHandler))
  MaxNumSGPRs -= std::min(MaxNumSGPRs, TRAP_NUM_SGPRS) ;
MaxNumSGPRs = alignDown(MaxNumSGPRs, getSGPRAllocGranule(Features));
return std::min(MaxNumSGPRs, AddressableNumSGPRs);

229–235

Why is this needed? Why is getAddressableNumSGPRs not returning the correct value for each target?

[kzhuravl]

lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp

229–235

I talked to Tony offline about this. I will do relevant changes after this change lands.

[wdng]

Address code reviews. Thank you Tony for such detailed comments!

[kzhuravl]

Rebase + add test

[t-tye]

LGTM

lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp

234

Remove space before ;

lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h

 
 namespace AMDGPU {
 
 namespace IsaInfo {
 
 enum {
   // The closed Vulkan driver sets 96, which limits the wave count to 8 but
   // doesn't spill SGPRs as much as when 80 is set.
-  FIXED_NUM_SGPRS_FOR_INIT_BUG = 96
+  FIXED_NUM_SGPRS_FOR_INIT_BUG = 96,
+  TRAP_NUM_SGPRS = 16
 };
 
 /// \brief Instruction set architecture version.
 struct IsaVersion {
   unsigned Major;
   unsigned Minor;
   unsigned Stepping;
 };

lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.cpp

if (Version.Major >= 8)
     return 102;
   return 104;
 }
 
 unsigned getMinNumSGPRs(const FeatureBitset &Features, unsigned WavesPerEU) {
   assert(WavesPerEU != 0);
 
   if (WavesPerEU >= getMaxWavesPerEU(Features))
     return 0;
-  unsigned MinNumSGPRs =
-      alignDown(getTotalNumSGPRs(Features) / (WavesPerEU + 1),
-                getSGPRAllocGranule(Features)) + 1;
+
+  unsigned MinNumSGPRs = getTotalNumSGPRs(Features) / (WavesPerEU + 1);
+  if (Features.test(FeatureTrapHandler))
+    MinNumSGPRs -= std::min(MinNumSGPRs, (unsigned)TRAP_NUM_SGPRS);
+  MinNumSGPRs = alignDown(MinNumSGPRs, getSGPRAllocGranule(Features)) + 1;
   return std::min(MinNumSGPRs, getAddressableNumSGPRs(Features));
 }
 
 unsigned getMaxNumSGPRs(const FeatureBitset &Features, unsigned WavesPerEU,
                         bool Addressable) {
   assert(WavesPerEU != 0);
 
   IsaVersion Version = getIsaVersion(Features);
-  unsigned MaxNumSGPRs = alignDown(getTotalNumSGPRs(Features) / WavesPerEU,
-                                   getSGPRAllocGranule(Features));
   unsigned AddressableNumSGPRs = getAddressableNumSGPRs(Features);
   if (Version.Major >= 8 && !Addressable)
     AddressableNumSGPRs = 112;
+  unsigned MaxNumSGPRs = getTotalNumSGPRs(Features) / WavesPerEU;
+  if (Features.test(FeatureTrapHandler))
+    MaxNumSGPRs -= std::min(MaxNumSGPRs, (unsigned)TRAP_NUM_SGPRS) ;
+  MaxNumSGPRs = alignDown(MaxNumSGPRs, getSGPRAllocGranule(Features));
   return std::min(MaxNumSGPRs, AddressableNumSGPRs);
 }
 
 unsigned getVGPRAllocGranule(const FeatureBitset &Features) {
   return 4;
 }
 
 unsigned getVGPREncodingGranule(const FeatureBitset &Features) {
   return getVGPRAllocGranule(Features);
 }