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[ConstantFolding] Support ptrtoaddr in cast folds #162480

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merged 2 commits into from
Oct 9, 2025
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Merged

[ConstantFolding] Support ptrtoaddr in cast folds #162480

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[ConstantFolding] Support ptrtoaddr in cast folds
nikic Oct 8, 2025
57dcb7d
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nikic Oct 9, 2025
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24 changes: 13 additions & 11 deletions llvm/lib/Analysis/ConstantFolding.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1495,30 +1495,31 @@ Constant *llvm::ConstantFoldCastOperand(unsigned Opcode, Constant *C,
default:
llvm_unreachable("Missing case");
case Instruction::PtrToAddr:
// TODO: Add some of the ptrtoint folds here as well.
break;
case Instruction::PtrToInt:
if (auto *CE = dyn_cast<ConstantExpr>(C)) {
Constant *FoldedValue = nullptr;
// If the input is a inttoptr, eliminate the pair. This requires knowing
// If the input is an inttoptr, eliminate the pair. This requires knowing
// the width of a pointer, so it can't be done in ConstantExpr::getCast.
if (CE->getOpcode() == Instruction::IntToPtr) {
// zext/trunc the inttoptr to pointer size.
FoldedValue = ConstantFoldIntegerCast(CE->getOperand(0),
DL.getIntPtrType(CE->getType()),
// zext/trunc the inttoptr to pointer/address size.
Type *MidTy = Opcode == Instruction::PtrToInt
? DL.getAddressType(CE->getType())
: DL.getIntPtrType(CE->getType());
FoldedValue = ConstantFoldIntegerCast(CE->getOperand(0), MidTy,
/*IsSigned=*/false, DL);
} else if (auto *GEP = dyn_cast<GEPOperator>(CE)) {
// If we have GEP, we can perform the following folds:
// (ptrtoint (gep null, x)) -> x
// (ptrtoint (gep (gep null, x), y) -> x + y, etc.
// (ptrtoint/ptrtoaddr (gep null, x)) -> x
// (ptrtoint/ptrtoaddr (gep (gep null, x), y) -> x + y, etc.
unsigned BitWidth = DL.getIndexTypeSizeInBits(GEP->getType());
APInt BaseOffset(BitWidth, 0);
auto *Base = cast<Constant>(GEP->stripAndAccumulateConstantOffsets(
DL, BaseOffset, /*AllowNonInbounds=*/true));
if (Base->isNullValue()) {
FoldedValue = ConstantInt::get(CE->getContext(), BaseOffset);
} else {
// ptrtoint (gep i8, Ptr, (sub 0, V)) -> sub (ptrtoint Ptr), V
// ptrtoint/ptrtoaddr (gep i8, Ptr, (sub 0, V))
// -> sub (ptrtoint/ptrtoaddr Ptr), V
if (GEP->getNumIndices() == 1 &&
GEP->getSourceElementType()->isIntegerTy(8)) {
auto *Ptr = cast<Constant>(GEP->getPointerOperand());
Expand All @@ -1528,12 +1529,13 @@ Constant *llvm::ConstantFoldCastOperand(unsigned Opcode, Constant *C,
Sub->getOpcode() == Instruction::Sub &&
Sub->getOperand(0)->isNullValue())
FoldedValue = ConstantExpr::getSub(
ConstantExpr::getPtrToInt(Ptr, IntIdxTy), Sub->getOperand(1));
ConstantExpr::getCast(Opcode, Ptr, IntIdxTy),
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I am not sure these folds are valid for unstable GC pointers, but since this has been like this for a long time and I have no detailed knowledge of GC pointer support I imagine it's fine.

Sub->getOperand(1));
}
}
}
if (FoldedValue) {
// Do a zext or trunc to get to the ptrtoint dest size.
// Do a zext or trunc to get to the ptrtoint/ptrtoaddr dest size.
return ConstantFoldIntegerCast(FoldedValue, DestTy, /*IsSigned=*/false,
DL);
}
Expand Down
46 changes: 41 additions & 5 deletions llvm/test/Transforms/InstCombine/ptrtoaddr.ll
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Original file line number Diff line number Diff line change
@@ -1,6 +1,14 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
; RUN: opt < %s -passes=instcombine -S | FileCheck %s
target datalayout = "p1:64:64:64:32"

; The ptrtoaddr folds are also valid for pointers that have external state.
target datalayout = "pe1:64:64:64:32"

@g = external global i8
@g2 = external global i8

@g.as1 = external addrspace(1) global i8
@g2.as1 = external addrspace(1) global i8

define i32 @ptrtoaddr_inttoptr_arg(i32 %a) {
; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_arg(
Expand All @@ -24,14 +32,14 @@ define i32 @ptrtoaddr_inttoptr() {

define i32 @ptrtoaddr_inttoptr_diff_size1() {
; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_diff_size1() {
; CHECK-NEXT: ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i64 -1 to ptr addrspace(1)) to i32)
; CHECK-NEXT: ret i32 -1
;
ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i64 -1 to ptr addrspace(1)) to i32)
}

define i32 @ptrtoaddr_inttoptr_diff_size2() {
; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_diff_size2() {
; CHECK-NEXT: ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i16 -1 to ptr addrspace(1)) to i32)
; CHECK-NEXT: ret i32 65535
;
ret i32 ptrtoaddr (ptr addrspace(1) inttoptr (i16 -1 to ptr addrspace(1)) to i32)
}
Expand All @@ -52,14 +60,42 @@ define i64 @ptr2addr2_inttoptr_noas2() {

define i64 @ptrtoaddr_inttoptr_noas_diff_size1() {
; CHECK-LABEL: define i64 @ptrtoaddr_inttoptr_noas_diff_size1() {
; CHECK-NEXT: ret i64 ptrtoaddr (ptr inttoptr (i32 -1 to ptr) to i64)
; CHECK-NEXT: ret i64 4294967295
;
ret i64 ptrtoaddr (ptr inttoptr (i32 -1 to ptr) to i64)
}

define i64 @ptrtoaddr_inttoptr_noas_diff_size2() {
; CHECK-LABEL: define i64 @ptrtoaddr_inttoptr_noas_diff_size2() {
; CHECK-NEXT: ret i64 ptrtoaddr (ptr inttoptr (i128 -1 to ptr) to i64)
; CHECK-NEXT: ret i64 -1
;
ret i64 ptrtoaddr (ptr inttoptr (i128 -1 to ptr) to i64)
}

define i64 @ptrtoaddr_gep_null() {
; CHECK-LABEL: define i64 @ptrtoaddr_gep_null() {
; CHECK-NEXT: ret i64 42
;
ret i64 ptrtoaddr (ptr getelementptr (i8, ptr null, i64 42) to i64)
}

define i32 @ptrtoaddr_gep_null_addrsize() {
; CHECK-LABEL: define i32 @ptrtoaddr_gep_null_addrsize() {
; CHECK-NEXT: ret i32 42
;
ret i32 ptrtoaddr (ptr addrspace(1) getelementptr (i8, ptr addrspace(1) null, i32 42) to i32)
}

define i64 @ptrtoaddr_gep_sub() {
; CHECK-LABEL: define i64 @ptrtoaddr_gep_sub() {
; CHECK-NEXT: ret i64 sub (i64 ptrtoaddr (ptr @g to i64), i64 ptrtoaddr (ptr @g2 to i64))
;
ret i64 ptrtoaddr (ptr getelementptr (i8, ptr @g, i64 sub (i64 0, i64 ptrtoaddr (ptr @g2 to i64))) to i64)
}

define i32 @ptrtoaddr_gep_sub_addrsize() {
; CHECK-LABEL: define i32 @ptrtoaddr_gep_sub_addrsize() {
; CHECK-NEXT: ret i32 sub (i32 ptrtoaddr (ptr addrspace(1) @g.as1 to i32), i32 ptrtoaddr (ptr addrspace(1) @g2.as1 to i32))
;
ret i32 ptrtoaddr (ptr addrspace(1) getelementptr (i8, ptr addrspace(1) @g.as1, i32 sub (i32 0, i32 ptrtoaddr (ptr addrspace(1) @g2.as1 to i32))) to i32)
}