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[IR] Handle trunc for ptrtoaddr(inttoptr) cast pair (#162842)

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For ptrtoint(inttoptr) and ptrtoaddr(inttoptr), handle the case where
the source and destination size do not match and convert to either zext
or trunc. We can't do this if the middle size is smaller than both
src/dest, because we'd have to perform an additional masking operation
in that case.

Most of these cases are handled by dint of ptrtoint/inttoptr size
canonicalization (so I added some unit tests instead). However, the
ptrtoaddr(inttoptr) case where the pointer size and address size differ
is relevant, as in that case the mismatch in integer sizes is canonical.
This commit is contained in:
Nikita Popov 2025-10-13 11:10:41 +02:00 committed by GitHub
parent ea251536d5
commit 4a3e0001e3
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GPG Key ID: B5690EEEBB952194
3 changed files with 50 additions and 11 deletions
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16
llvm/lib/IR/Instructions.cpp
View File

@ -2965,8 +2965,7 @@ unsigned CastInst::isEliminableCastPair(Instruction::CastOps firstOp,
// zext, sext -> zext, because sext can't sign extend after zext
return Instruction::ZExt;
case 11: {
// inttoptr, ptrtoint/ptrtoaddr -> bitcast if SrcSize<=PtrSize/AddrSize
// and SrcSize==DstSize
// inttoptr, ptrtoint/ptrtoaddr -> integer cast
if (!DL)
return 0;
unsigned MidSize = secondOp == Instruction::PtrToAddr
@ -2974,10 +2973,15 @@ unsigned CastInst::isEliminableCastPair(Instruction::CastOps firstOp,
: DL->getPointerTypeSizeInBits(MidTy);
unsigned SrcSize = SrcTy->getScalarSizeInBits();
unsigned DstSize = DstTy->getScalarSizeInBits();
// TODO: Could also produce zext or trunc here.
if (SrcSize <= MidSize && SrcSize == DstSize)
return Instruction::BitCast;
return 0;
// If the middle size is smaller than both source and destination,
// an additional masking operation would be required.
if (MidSize < SrcSize && MidSize < DstSize)
return 0;
if (DstSize < SrcSize)
return Instruction::Trunc;
if (DstSize > SrcSize)
return Instruction::ZExt;
return Instruction::BitCast;
}
case 12:
// addrspacecast, addrspacecast -> bitcast, if SrcAS == DstAS

5
llvm/test/Transforms/InstCombine/ptrtoaddr.ll
View File

@ -23,10 +23,7 @@ define i64 @ptrtoaddr_inttoptr_arg(i64 %a) {
define i32 @ptrtoaddr_inttoptr_arg_addrsize(i32 %a) {
; CHECK-LABEL: define i32 @ptrtoaddr_inttoptr_arg_addrsize(
; CHECK-SAME: i32 [[A:%.*]]) {
; CHECK-NEXT: [[TMP1:%.*]] = zext i32 [[A]] to i64
; CHECK-NEXT: [[TOPTR:%.*]] = inttoptr i64 [[TMP1]] to ptr addrspace(1)
; CHECK-NEXT: [[TOADDR:%.*]] = ptrtoaddr ptr addrspace(1) [[TOPTR]] to i32
; CHECK-NEXT: ret i32 [[TOADDR]]
; CHECK-NEXT: ret i32 [[A]]
;
%toptr = inttoptr i32 %a to ptr addrspace(1)
%toaddr = ptrtoaddr ptr addrspace(1) %toptr to i32

40
llvm/unittests/IR/InstructionsTest.cpp
View File

@ -606,12 +606,14 @@ TEST(InstructionTest, ConstrainedTrans) {
TEST(InstructionsTest, isEliminableCastPair) {
LLVMContext C;
DataLayout DL1("p1:32:32");
DataLayout DL1("p1:32:32-p2:64:64:64:32");
Type *Int16Ty = Type::getInt16Ty(C);
Type *Int32Ty = Type::getInt32Ty(C);
Type *Int64Ty = Type::getInt64Ty(C);
Type *PtrTy64 = PointerType::get(C, 0);
Type *PtrTy32 = PointerType::get(C, 1);
Type *PtrTy64_32 = PointerType::get(C, 2);
// Source and destination pointers have same size -> bitcast.
EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::PtrToInt,
@ -637,6 +639,42 @@ TEST(InstructionsTest, isEliminableCastPair) {
Int64Ty, &DL1),
0U);
// Destination larger than source. Pointer type same as destination.
EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
CastInst::PtrToInt, Int16Ty, PtrTy64,
Int64Ty, &DL1),
CastInst::ZExt);
// Destination larger than source. Pointer type different from destination.
EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
CastInst::PtrToInt, Int16Ty, PtrTy32,
Int64Ty, &DL1),
CastInst::ZExt);
// Destination smaller than source. Pointer type same as source.
EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
CastInst::PtrToInt, Int64Ty, PtrTy64,
Int16Ty, &DL1),
CastInst::Trunc);
// Destination smaller than source. Pointer type different from source.
EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
CastInst::PtrToInt, Int64Ty, PtrTy32,
Int16Ty, &DL1),
CastInst::Trunc);
// ptrtoaddr with address size != pointer size. Truncating case.
EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
CastInst::PtrToAddr, Int64Ty,
PtrTy64_32, Int32Ty, &DL1),
CastInst::Trunc);
// ptrtoaddr with address size != pointer size. Non-truncating case.
EXPECT_EQ(CastInst::isEliminableCastPair(CastInst::IntToPtr,
CastInst::PtrToAddr, Int32Ty,
PtrTy64_32, Int32Ty, &DL1),
CastInst::BitCast);
// Test that we don't eliminate bitcasts between different address spaces,
// or if we don't have available pointer size information.
DataLayout DL2("e-p:32:32:32-p1:16:16:16-p2:64:64:64-i1:8:8-i8:8:8-i16:16:16"