[llvm] [AMDGPU][GlobaISel] wrap the load-splitting code in RegBank selection with condition (PR #98966)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Gang Chen (cmc-rep)

<details>
<summary>Changes</summary>

The load-splitting code in RegBank selection is only relevant to those listed address-spaces because there are cases in those address-spaces in which we are not sure how far to split during legalization

---
Full diff: https://github.com/llvm/llvm-project/pull/98966.diff


1 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp (+20-14) 


``````````diff
diff --git a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
index 9e7694f41d6b8..71b88c011b6c2 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
@@ -1059,6 +1059,7 @@ bool AMDGPURegisterBankInfo::applyMappingLoad(
   Register DstReg = MI.getOperand(0).getReg();
   const LLT LoadTy = MRI.getType(DstReg);
   unsigned LoadSize = LoadTy.getSizeInBits();
+  MachineMemOperand *MMO = *MI.memoperands_begin();
   const unsigned MaxNonSmrdLoadSize = 128;
 
   const RegisterBank *DstBank =
@@ -1069,7 +1070,6 @@ bool AMDGPURegisterBankInfo::applyMappingLoad(
     if (LoadSize != 32 && (LoadSize != 96 || Subtarget.hasScalarDwordx3Loads()))
       return false;
 
-    MachineMemOperand *MMO = *MI.memoperands_begin();
     const unsigned MemSize = 8 * MMO->getSize().getValue();
     // Scalar loads of size 8 or 16 bit with proper alignment may be widened to
     // 32 bit. Check to see if we need to widen the memory access, 8 or 16 bit
@@ -1142,25 +1142,31 @@ bool AMDGPURegisterBankInfo::applyMappingLoad(
   if (SrcRegs.empty())
     SrcRegs.push_back(MI.getOperand(1).getReg());
 
-  assert(LoadSize % MaxNonSmrdLoadSize == 0);
-
   // RegBankSelect only emits scalar types, so we need to reset the pointer
   // operand to a pointer type.
   Register BasePtrReg = SrcRegs[0];
   LLT PtrTy = MRI.getType(MI.getOperand(1).getReg());
   MRI.setType(BasePtrReg, PtrTy);
 
-  unsigned NumSplitParts = LoadTy.getSizeInBits() / MaxNonSmrdLoadSize;
-  const LLT LoadSplitTy = LoadTy.divide(NumSplitParts);
-  ApplyRegBankMapping O(B, *this, MRI, &AMDGPU::VGPRRegBank);
-  LegalizerHelper Helper(B.getMF(), O, B);
-
-  if (LoadTy.isVector()) {
-    if (Helper.fewerElementsVector(MI, 0, LoadSplitTy) != LegalizerHelper::Legalized)
-      return false;
-  } else {
-    if (Helper.narrowScalar(MI, 0, LoadSplitTy) != LegalizerHelper::Legalized)
-      return false;
+  // the following are the loads not splitted enough during legalization
+  // because it was not clear they are smem-load or vmem-load
+  if (MMO->getAddrSpace() == AMDGPUAS::GLOBAL_ADDRESS ||
+      MMO->getAddrSpace() == AMDGPUAS::CONSTANT_ADDRESS ||
+      MMO->getAddrSpace() == AMDGPUAS::CONSTANT_ADDRESS_32BIT ||
+      MMO->getAddrSpace() == AMDGPUAS::BUFFER_RESOURCE) {
+    assert(LoadSize % MaxNonSmrdLoadSize == 0);
+    unsigned NumSplitParts = LoadTy.getSizeInBits() / MaxNonSmrdLoadSize;
+    const LLT LoadSplitTy = LoadTy.divide(NumSplitParts);
+    ApplyRegBankMapping O(B, *this, MRI, &AMDGPU::VGPRRegBank);
+    LegalizerHelper Helper(B.getMF(), O, B);
+    if (LoadTy.isVector()) {
+      if (Helper.fewerElementsVector(MI, 0, LoadSplitTy) !=
+          LegalizerHelper::Legalized)
+        return false;
+    } else {
+      if (Helper.narrowScalar(MI, 0, LoadSplitTy) != LegalizerHelper::Legalized)
+        return false;
+    }
   }
 
   MRI.setRegBank(DstReg, AMDGPU::VGPRRegBank);

``````````

</details>


https://github.com/llvm/llvm-project/pull/98966