[llvm] [SPIR-V] Add OpUntypedVariableLengthArrayINTEL support for SPV_INTEL_variable_length_array (PR #224756)

[Qi Ye via llvm-commits]

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@@ -7043,11 +7043,30 @@ bool SPIRVInstructionSelector::selectAllocaArray(Register ResVReg,
   // there was an allocation size parameter to the allocation instruction
   // that is not 1
   MachineBasicBlock &BB = *I.getParent();
-  BuildMI(BB, I, I.getDebugLoc(), TII.get(SPIRV::OpVariableLengthArrayINTEL))
-      .addDef(ResVReg)
-      .addUse(GR.getSPIRVTypeID(ResType))
-      .addUse(I.getOperand(2).getReg())
-      .constrainAllUses(TII, TRI, RBI);
+
+  bool UseUntypedPointers =
+      ResType->getOpcode() == SPIRV::OpTypeUntypedPointerKHR;
+  unsigned Opcode = UseUntypedPointers
+                        ? SPIRV::OpUntypedVariableLengthArrayINTEL
+                        : SPIRV::OpVariableLengthArrayINTEL;
+
+  auto MIB = BuildMI(BB, I, I.getDebugLoc(), TII.get(Opcode))
+                 .addDef(ResVReg)
+                 .addUse(GR.getSPIRVTypeID(ResType));
+
+  // OpUntypedVariableLengthArrayINTEL takes an explicit Element Type <id>
+  // right after the result type
+  if (UseUntypedPointers) {
+    SPIRVTypeInst ElementType = GR.getUntypedPtrElementType(ResVReg);
+    assert(ElementType &&
+           "untyped variable length array result must have a recorded element "
+           "type");
----------------
Qi-Ye-079 wrote:

Use assert here because I don't think the `ElementType==nullptr` case is reachable. It's translated from `alloca` which always carries the element type, so the `ElementType` should always be known. This should be an invariant pre-condition that always hold. I'm not sure if VLA is allowed in shaders, but both `SPV_INTEL_variable_length_array` and `SPV_KHR_untyped_pointers` are defined for OpenCL env only in SPIRVSymbolicOperands.td, so we don't need to consider shader env here.
About the `diagnoseUnsupported` in `selectFrameIndex`, I think it's never reachable either, and there's no test to cover it.

https://github.com/llvm/llvm-project/pull/224756