[Backport to 16] [SPIR-V 1.2] SPIRVReader: Add AlignmentId support (#2869) (#2887)

If there is no `OpDecorate .. Alignment` in the input, see if there is
an `OpDecorateId .. AlignmentId` and take the alignment from the
referenced constant instead.

Once `AlignmentId` has been translated to LLVM IR, it is
indistinguishable from an (non-ID) `Alignment` decoration.

(cherry picked from commit da1731b)

Author: svenvh

lib/SPIRV/SPIRVReader.cpp

@@ -285,6 +285,29 @@ Value *SPIRVToLLVM::mapFunction(SPIRVFunction *BF, Function *F) {
   return F;
 }
 
+std::optional<uint64_t> SPIRVToLLVM::transIdAsConstant(SPIRVId Id) {
+  auto *V = BM->get<SPIRVValue>(Id);
+  const auto *ConstValue =
+      dyn_cast<ConstantInt>(transValue(V, nullptr, nullptr));
+  if (!ConstValue)
+    return {};
+  return ConstValue->getZExtValue();
+}
+
+std::optional<uint64_t> SPIRVToLLVM::getAlignment(SPIRVValue *V) {
+  SPIRVWord AlignmentBytes = 0;
+  if (V->hasAlignment(&AlignmentBytes)) {
+    return AlignmentBytes;
+  }
+
+  // If there was no Alignment decoration, look for AlignmentId instead.
+  SPIRVId AlignId;
+  if (V->hasDecorateId(DecorationAlignmentId, 0, &AlignId)) {
+    return transIdAsConstant(AlignId);
+  }
+  return {};
+}
+
 Type *SPIRVToLLVM::transFPType(SPIRVType *T) {
   switch (T->getFloatBitWidth()) {
   case 16:
@@ -3011,9 +3034,9 @@ void SPIRVToLLVM::transFunctionAttrs(SPIRVFunction *BF, Function *F) {
     SPIRVWord MaxOffset = 0;
     if (BA->hasDecorate(DecorationMaxByteOffset, 0, &MaxOffset))
       Builder.addDereferenceableAttr(MaxOffset);
-    SPIRVWord AlignmentBytes = 0;
-    if (BA->hasAlignment(&AlignmentBytes))
-      Builder.addAlignmentAttr(AlignmentBytes);
+    if (auto Alignment = getAlignment(BA)) {
+      Builder.addAlignmentAttr(*Alignment);
+    }
     I->addAttrs(Builder);
   }
   BF->foreachReturnValueAttr([&](SPIRVFuncParamAttrKind Kind) {
@@ -4691,16 +4714,14 @@ bool SPIRVToLLVM::transFPGAFunctionMetadata(SPIRVFunction *BF, Function *F) {
 }
 
 bool SPIRVToLLVM::transAlign(SPIRVValue *BV, Value *V) {
-  if (auto AL = dyn_cast<AllocaInst>(V)) {
-    SPIRVWord Align = 0;
-    if (BV->hasAlignment(&Align))
-      AL->setAlignment(llvm::Align(Align));
+  if (auto *AL = dyn_cast<AllocaInst>(V)) {
+    if (auto Align = getAlignment(BV))
+      AL->setAlignment(llvm::Align(*Align));
     return true;
   }
-  if (auto GV = dyn_cast<GlobalVariable>(V)) {
-    SPIRVWord Align = 0;
-    if (BV->hasAlignment(&Align))
-      GV->setAlignment(MaybeAlign(Align));
+  if (auto *GV = dyn_cast<GlobalVariable>(V)) {
+    if (auto Align = getAlignment(BV))
+      GV->setAlignment(MaybeAlign(*Align));
     return true;
   }
   return true;

lib/SPIRV/SPIRVReader.h

@@ -214,6 +214,13 @@ class SPIRVToLLVM : private BuiltinCallHelper {
 
   bool isDirectlyTranslatedToOCL(Op OpCode) const;
   MDString *transOCLKernelArgTypeName(SPIRVFunctionParameter *);
+
+  // Attempt to translate Id as a (specialization) constant.
+  std::optional<uint64_t> transIdAsConstant(SPIRVId Id);
+
+  // Return the value of an Alignment or AlignmentId decoration for V.
+  std::optional<uint64_t> getAlignment(SPIRVValue *V);
+
   Value *mapFunction(SPIRVFunction *BF, Function *F);
   Value *getTranslatedValue(SPIRVValue *BV);
   IntrinsicInst *getLifetimeStartIntrinsic(Instruction *I);

test/AlignmentId.spvasm

@@ -0,0 +1,34 @@
+; REQUIRES: spirv-as
+
+; RUN: spirv-as %s --target-env spv1.2 -o %t.spv
+; RUN: spirv-val %t.spv
+; RUN: llvm-spirv -r -o %t.rev.bc %t.spv
+; RUN: llvm-dis %t.rev.bc -o - | FileCheck %s
+
+               OpCapability Addresses
+               OpCapability Linkage
+               OpCapability Kernel
+               OpMemoryModel Physical64 OpenCL
+               OpEntryPoint Kernel %fn "testAlignmentId"
+               OpName %p "p"
+               OpDecorate %x LinkageAttributes "x" Export
+               OpDecorateId %x AlignmentId %al
+               OpDecorateId %p AlignmentId %al_spec
+       %void = OpTypeVoid
+       %uint = OpTypeInt 32 0
+        %ptr = OpTypePointer CrossWorkgroup %uint
+       %fnTy = OpTypeFunction %void %ptr
+         %al = OpConstant %uint 16
+    %al_spec = OpSpecConstantOp %uint IAdd %al %al
+    %uint_42 = OpConstant %uint 42
+; Verify alignment of variable.
+; CHECK: @x = addrspace(1) global i32 42, align 16
+          %x = OpVariable %ptr CrossWorkgroup %uint_42
+
+         %fn = OpFunction %void None %fnTy
+; Verify alignment of function parameter.
+; CHECK: define spir_kernel void @testAlignmentId(ptr addrspace(1) align 32 %p)
+          %p = OpFunctionParameter %ptr
+      %entry = OpLabel
+               OpReturn
+               OpFunctionEnd