[llvm] [GlobalISel][IRTranslator] Lower ptr/non-ptr bitcasts via G_INTTOPTR/G_PTRTOINT (PR #203335)

[Petar Avramovic via llvm-commits]

================
@@ -1596,16 +1598,71 @@ bool IRTranslator::translateBitCast(const User &U,
     return translateCopy(U, *U.getOperand(0), MIRBuilder);
   }
 
-  // Only the scalar byte<->ptr crossing is redirected to G_INTTOPTR/G_PTRTOINT,
-  // which is the well-typed MIR shape for that boundary. Vector byte<->ptr
-  // (e.g. <N x b32> -> ptr produced by mixed-type load coalescing) and other
-  // legacy ptr/non-ptr IR bitcasts (AMDGPU iN<->p3 kernarg packing, etc.)
-  // keep their historical G_BITCAST lowering — G_INTTOPTR has no vector-src
-  // -> scalar-ptr form, and downstream passes already handle G_BITCAST.
-  if (DstTy->isPointerTy() && SrcTy->isByteTy())
-    return translateCast(TargetOpcode::G_INTTOPTR, U, MIRBuilder);
-  if (SrcTy->isPointerTy() && DstTy->isByteTy())
-    return translateCast(TargetOpcode::G_PTRTOINT, U, MIRBuilder);
+  // Emit G_INTTOPTR
+  if (!SrcTy->isPointerTy() && DstTy->isPointerTy()) {
+    if (DstTyBits == SrcTyBits) {
+      if (!mayTranslateUserTypes(U))
+        return false;
+
+      uint32_t Flags = 0;
+      if (const Instruction *I = dyn_cast<Instruction>(&U))
+        Flags = MachineInstr::copyFlagsFromInstruction(*I);
+
+      Register SrcReg = getOrCreateVReg(*U.getOperand(0));
+      Register DstReg = getOrCreateVReg(U);
+      MachineRegisterInfo &MRI = *MIRBuilder.getMRI();
+      LLT IntLLT = LLT::scalar(DstTyBits);
+      LLT SrcLLT = MRI.getType(SrcReg);
+
+      // Prefer IR integer check; also accept when the operand is already the
+      // pointer-sized scalar LLT (e.g. i64 value lowered to s64) so we never
+      // emit G_BITCAST sN -> sN, which MachineVerifier rejects.
+      if ((SrcTy->isIntegerTy() &&
+           cast<IntegerType>(SrcTy)->getBitWidth() == DstTyBits) ||
+          SrcLLT == IntLLT) {
+        MIRBuilder.buildInstr(TargetOpcode::G_INTTOPTR, {DstReg}, {SrcReg},
+                              Flags);
+        return true;
+      }
+
+      auto IntVal = MIRBuilder.buildBitcast(IntLLT, SrcReg);
+      MIRBuilder.buildInstr(TargetOpcode::G_INTTOPTR, {DstReg},
+                            {IntVal.getReg(0)}, Flags);
+      return true;
+    }
----------------
petar-avramovic wrote:

should be able to simplify
if(...){
Src = build-Bitcast
}

build-IntToPtr(Src)
return true

https://github.com/llvm/llvm-project/pull/203335