[llvm] [InferAddressSpaces] Extend undef pointer operand support to phi inst (PR #159548)
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Thu Sep 18 03:27:08 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-amdgpu
Author: Wenju He (wenju-he)
<details>
<summary>Changes</summary>
Previously undef pointer operand is only supported for select inst, where undef in generic AS behaves like `take the other side`.
This PR extends the support to other instructions, e.g. phi inst. Defer joining and inferring constant pointer operand until all other operand AS states considered.
---
Full diff: https://github.com/llvm/llvm-project/pull/159548.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp (+39-61)
- (added) llvm/test/Transforms/InferAddressSpaces/AMDGPU/phi-undef.ll (+36)
``````````diff
diff --git a/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp b/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
index a097d338a42ca..fffed5c7ce9aa 100644
--- a/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
+++ b/llvm/lib/Transforms/Scalar/InferAddressSpaces.cpp
@@ -1002,70 +1002,48 @@ bool InferAddressSpacesImpl::updateAddressSpace(
// isAddressExpression should guarantee that V is an operator or an argument.
assert(isa<Operator>(V) || isa<Argument>(V));
- if (isa<Operator>(V) &&
- cast<Operator>(V).getOpcode() == Instruction::Select) {
- const Operator &Op = cast<Operator>(V);
- Value *Src0 = Op.getOperand(1);
- Value *Src1 = Op.getOperand(2);
-
- auto I = InferredAddrSpace.find(Src0);
- unsigned Src0AS = (I != InferredAddrSpace.end())
- ? I->second
- : Src0->getType()->getPointerAddressSpace();
-
- auto J = InferredAddrSpace.find(Src1);
- unsigned Src1AS = (J != InferredAddrSpace.end())
- ? J->second
- : Src1->getType()->getPointerAddressSpace();
-
- auto *C0 = dyn_cast<Constant>(Src0);
- auto *C1 = dyn_cast<Constant>(Src1);
-
- // If one of the inputs is a constant, we may be able to do a constant
- // addrspacecast of it. Defer inferring the address space until the input
- // address space is known.
- if ((C1 && Src0AS == UninitializedAddressSpace) ||
- (C0 && Src1AS == UninitializedAddressSpace))
- return false;
-
- if (C0 && isSafeToCastConstAddrSpace(C0, Src1AS))
- NewAS = Src1AS;
- else if (C1 && isSafeToCastConstAddrSpace(C1, Src0AS))
- NewAS = Src0AS;
- else
- NewAS = joinAddressSpaces(Src0AS, Src1AS);
+ unsigned AS = TTI->getAssumedAddrSpace(&V);
+ if (AS != UninitializedAddressSpace) {
+ // Use the assumed address space directly.
+ NewAS = AS;
} else {
- unsigned AS = TTI->getAssumedAddrSpace(&V);
- if (AS != UninitializedAddressSpace) {
- // Use the assumed address space directly.
- NewAS = AS;
- } else {
- // Otherwise, infer the address space from its pointer operands.
- for (Value *PtrOperand : getPointerOperands(V, *DL, TTI)) {
- auto I = InferredAddrSpace.find(PtrOperand);
- unsigned OperandAS;
- if (I == InferredAddrSpace.end()) {
- OperandAS = PtrOperand->getType()->getPointerAddressSpace();
- if (OperandAS == FlatAddrSpace) {
- // Check AC for assumption dominating V.
- unsigned AS = getPredicatedAddrSpace(*PtrOperand, &V);
- if (AS != UninitializedAddressSpace) {
- LLVM_DEBUG(dbgs()
- << " deduce operand AS from the predicate addrspace "
- << AS << '\n');
- OperandAS = AS;
- // Record this use with the predicated AS.
- PredicatedAS[std::make_pair(&V, PtrOperand)] = OperandAS;
- }
+ // Otherwise, infer the address space from its pointer operands.
+ SmallVector<Constant *, 2> ConstantPtrOps;
+ for (Value *PtrOperand : getPointerOperands(V, *DL, TTI)) {
+ auto I = InferredAddrSpace.find(PtrOperand);
+ unsigned OperandAS;
+ if (I == InferredAddrSpace.end()) {
+ OperandAS = PtrOperand->getType()->getPointerAddressSpace();
+ if (auto *C = dyn_cast<Constant>(PtrOperand);
+ C && OperandAS == FlatAddrSpace) {
+ ConstantPtrOps.push_back(C);
+ continue;
+ }
+ if (OperandAS == FlatAddrSpace) {
+ // Check AC for assumption dominating V.
+ unsigned AS = getPredicatedAddrSpace(*PtrOperand, &V);
+ if (AS != UninitializedAddressSpace) {
+ LLVM_DEBUG(dbgs()
+ << " deduce operand AS from the predicate addrspace "
+ << AS << '\n');
+ OperandAS = AS;
+ // Record this use with the predicated AS.
+ PredicatedAS[std::make_pair(&V, PtrOperand)] = OperandAS;
}
- } else
- OperandAS = I->second;
+ }
+ } else
+ OperandAS = I->second;
- // join(flat, *) = flat. So we can break if NewAS is already flat.
- NewAS = joinAddressSpaces(NewAS, OperandAS);
- if (NewAS == FlatAddrSpace)
- break;
- }
+ // join(flat, *) = flat. So we can break if NewAS is already flat.
+ NewAS = joinAddressSpaces(NewAS, OperandAS);
+ if (NewAS == FlatAddrSpace)
+ break;
+ }
+ if (NewAS != FlatAddrSpace && NewAS != UninitializedAddressSpace) {
+ if (any_of(ConstantPtrOps, [&](Constant *C) {
+ return !isSafeToCastConstAddrSpace(C, NewAS);
+ }))
+ NewAS = FlatAddrSpace;
}
}
diff --git a/llvm/test/Transforms/InferAddressSpaces/AMDGPU/phi-undef.ll b/llvm/test/Transforms/InferAddressSpaces/AMDGPU/phi-undef.ll
new file mode 100644
index 0000000000000..c1fd05ceb8a4e
--- /dev/null
+++ b/llvm/test/Transforms/InferAddressSpaces/AMDGPU/phi-undef.ll
@@ -0,0 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900 -S -passes=infer-address-spaces %s | FileCheck %s
+
+define void @phi_undef(ptr addrspace(1) %arg, <2 x ptr addrspace(1)> %arg1) {
+; CHECK-LABEL: @phi_undef(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[TMP0:%.*]] = call i1 @is_leader()
+; CHECK-NEXT: br i1 [[TMP0]], label [[LEADER:%.*]], label [[MERGE:%.*]]
+; CHECK: leader:
+; CHECK-NEXT: br label [[MERGE]]
+; CHECK: merge:
+; CHECK-NEXT: [[I:%.*]] = phi ptr addrspace(1) [ [[ARG:%.*]], [[LEADER]] ], [ undef, [[ENTRY:%.*]] ]
+; CHECK-NEXT: [[I2:%.*]] = phi <2 x ptr addrspace(1)> [ [[ARG1:%.*]], [[LEADER]] ], [ undef, [[ENTRY]] ]
+; CHECK-NEXT: [[TMP1:%.*]] = addrspacecast <2 x ptr addrspace(1)> [[I2]] to <2 x ptr>
+; CHECK-NEXT: [[J:%.*]] = load i8, ptr addrspace(1) [[I]], align 1
+; CHECK-NEXT: [[J1:%.*]] = icmp eq <2 x ptr> [[TMP1]], zeroinitializer
+; CHECK-NEXT: ret void
+;
+entry:
+ %0 = call i1 @is_leader()
+ br i1 %0, label %leader, label %merge
+
+leader:
+ %cast = addrspacecast ptr addrspace(1) %arg to ptr
+ %cast1 = addrspacecast <2 x ptr addrspace(1)> %arg1 to <2 x ptr>
+ br label %merge
+
+merge:
+ %i = phi ptr [%cast, %leader], [undef, %entry]
+ %i1 = phi <2 x ptr> [%cast1, %leader], [undef, %entry]
+ %j = load i8, ptr %i, align 1
+ %j1 = icmp eq <2 x ptr> %i1, zeroinitializer
+ ret void
+}
+
+declare i1 @is_leader()
``````````
</details>
https://github.com/llvm/llvm-project/pull/159548
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