From 1639578af2ba688424813ee272f06afddb9bfbd3 Mon Sep 17 00:00:00 2001 From: Krzysztof Drewniak Date: Tue, 20 May 2025 18:09:19 +0000 Subject: [PATCH 1/2] [AMDGPU][LowerBufferFatPointers] Handle addrspacecast null to p7 Some application code operating on generic pointers (that then gete initialized to buffer fat pointers) may perform tests against nullptr. After address space inference, this results in comparisons against `addrspacecast (ptr null to ptr addrspace(7))`, which were crashing. However, while general casts to ptr addrspace(7) from generic pointers aren't supposted, it is possible to cast null pointers to the all-zerose bufer resource and 0 offset, which this patch adds. It also adds a TODO for casting _out_ of buffer resources, which isn't implemented here but could be. --- .../AMDGPU/AMDGPULowerBufferFatPointers.cpp | 23 ++++++++++--- .../lower-buffer-fat-pointers-pointer-ops.ll | 32 +++++++++++++++++++ 2 files changed, 51 insertions(+), 4 deletions(-) diff --git a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp index 275b3a6f16e54..fe873508f46d2 100644 --- a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp +++ b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp @@ -1980,6 +1980,8 @@ PtrParts SplitPtrStructs::visitIntToPtrInst(IntToPtrInst &IP) { } PtrParts SplitPtrStructs::visitAddrSpaceCastInst(AddrSpaceCastInst &I) { + // TODO(krzysz00): handle casts from ptr addrspace(7) to global pointers + // by computing the effective address. if (!isSplitFatPtr(I.getType())) return {nullptr, nullptr}; IRB.SetInsertPoint(&I); @@ -1990,11 +1992,24 @@ PtrParts SplitPtrStructs::visitAddrSpaceCastInst(AddrSpaceCastInst &I) { SplitUsers.insert(&I); return {Rsrc, Off}; } - if (I.getSrcAddressSpace() != AMDGPUAS::BUFFER_RESOURCE) - report_fatal_error("Only buffer resources (addrspace 8) can be cast to " - "buffer fat pointers (addrspace 7)"); - Type *OffTy = cast(I.getType())->getElementType(1); + + auto *ResTy = cast(I.getType()); + Type *RsrcTy = ResTy->getElementType(0); + Type *OffTy = ResTy->getElementType(1); Value *ZeroOff = Constant::getNullValue(OffTy); + + // Special case for null pointers, which can be created by address space + // propagation. + auto *InConst = dyn_cast(In); + if (InConst && InConst->isNullValue()) { + Value *NullRsrc = Constant::getNullValue(RsrcTy); + SplitUsers.insert(&I); + return {NullRsrc, ZeroOff}; + } + + if (I.getSrcAddressSpace() != AMDGPUAS::BUFFER_RESOURCE) + report_fatal_error("Only buffer resources (addrspace 8) and null pointers " + "can be cast to buffer fat pointers (addrspace 7)"); SplitUsers.insert(&I); return {In, ZeroOff}; } diff --git a/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll b/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll index fd5bf579cdeb2..cc5e2c833cc39 100644 --- a/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll +++ b/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll @@ -332,6 +332,38 @@ define <2 x ptr addrspace(7)> @addrspacecast_vec(<2 x ptr addrspace(8)> %buf) { ret <2 x ptr addrspace(7)> %ret } +define ptr addrspace(7) @addrspacecast_null() { +; CHECK-LABEL: define { ptr addrspace(8), i32 } @addrspacecast_null +; CHECK-SAME: () #[[ATTR0]] { +; CHECK-NEXT: ret { ptr addrspace(8), i32 } zeroinitializer +; + %ret = addrspacecast ptr null to ptr addrspace(7) + ret ptr addrspace(7) %ret +} + +define <2 x ptr addrspace(7)> @addrspacecast_null_vec() { +; CHECK-LABEL: define { <2 x ptr addrspace(8)>, <2 x i32> } @addrspacecast_null_vec +; CHECK-SAME: () #[[ATTR0]] { +; CHECK-NEXT: ret { <2 x ptr addrspace(8)>, <2 x i32> } zeroinitializer +; + %ret = addrspacecast <2 x ptr> zeroinitializer to <2 x ptr addrspace(7)> + ret <2 x ptr addrspace(7)> %ret +} + +define i1 @test_null(ptr addrspace(7) %p) { +; CHECK-LABEL: define i1 @test_null +; CHECK-SAME: ({ ptr addrspace(8), i32 } [[P:%.*]]) #[[ATTR0]] { +; CHECK-NEXT: [[P_RSRC:%.*]] = extractvalue { ptr addrspace(8), i32 } [[P]], 0 +; CHECK-NEXT: [[P_OFF:%.*]] = extractvalue { ptr addrspace(8), i32 } [[P]], 1 +; CHECK-NEXT: [[IS_NULL_RSRC:%.*]] = icmp eq ptr addrspace(8) [[P_RSRC]], null +; CHECK-NEXT: [[IS_NULL_OFF:%.*]] = icmp eq i32 [[P_OFF]], 0 +; CHECK-NEXT: [[IS_NULL:%.*]] = and i1 [[IS_NULL_RSRC]], [[IS_NULL_OFF]] +; CHECK-NEXT: ret i1 [[IS_NULL]] +; + %is.null = icmp eq ptr addrspace(7) %p, addrspacecast (ptr null to ptr addrspace(7)) + ret i1 %is.null +} + declare ptr addrspace(7) @llvm.amdgcn.make.buffer.rsrc.p7.p1(ptr addrspace(1), i16, i32, i32) define ptr addrspace(7) @make_buffer_rsrc(ptr addrspace(1) %buf, i16 %stride, i32 %numRecords, i32 %flags) { From 68dac67476bbcdbbdde89fd8157264915dc5ab40 Mon Sep 17 00:00:00 2001 From: Krzysztof Drewniak Date: Tue, 20 May 2025 18:27:11 +0000 Subject: [PATCH 2/2] Undef and poison --- .../AMDGPU/AMDGPULowerBufferFatPointers.cpp | 21 ++++++++--- .../lower-buffer-fat-pointers-pointer-ops.ll | 36 +++++++++++++++++++ 2 files changed, 53 insertions(+), 4 deletions(-) diff --git a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp index fe873508f46d2..20ccdcaa0e9a0 100644 --- a/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp +++ b/llvm/lib/Target/AMDGPU/AMDGPULowerBufferFatPointers.cpp @@ -1998,18 +1998,31 @@ PtrParts SplitPtrStructs::visitAddrSpaceCastInst(AddrSpaceCastInst &I) { Type *OffTy = ResTy->getElementType(1); Value *ZeroOff = Constant::getNullValue(OffTy); - // Special case for null pointers, which can be created by address space - // propagation. + // Special case for null pointers, undef, and poison, which can be created by + // address space propagation. auto *InConst = dyn_cast(In); if (InConst && InConst->isNullValue()) { Value *NullRsrc = Constant::getNullValue(RsrcTy); SplitUsers.insert(&I); return {NullRsrc, ZeroOff}; } + if (isa(In)) { + Value *PoisonRsrc = PoisonValue::get(RsrcTy); + Value *PoisonOff = PoisonValue::get(OffTy); + SplitUsers.insert(&I); + return {PoisonRsrc, PoisonOff}; + } + if (isa(In)) { + Value *UndefRsrc = UndefValue::get(RsrcTy); + Value *UndefOff = UndefValue::get(OffTy); + SplitUsers.insert(&I); + return {UndefRsrc, UndefOff}; + } if (I.getSrcAddressSpace() != AMDGPUAS::BUFFER_RESOURCE) - report_fatal_error("Only buffer resources (addrspace 8) and null pointers " - "can be cast to buffer fat pointers (addrspace 7)"); + report_fatal_error( + "only buffer resources (addrspace 8) and null/poison pointers can be " + "cast to buffer fat pointers (addrspace 7)"); SplitUsers.insert(&I); return {In, ZeroOff}; } diff --git a/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll b/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll index cc5e2c833cc39..63c0463149b79 100644 --- a/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll +++ b/llvm/test/CodeGen/AMDGPU/lower-buffer-fat-pointers-pointer-ops.ll @@ -364,6 +364,42 @@ define i1 @test_null(ptr addrspace(7) %p) { ret i1 %is.null } +define ptr addrspace(7) @addrspacecast_undef() { +; CHECK-LABEL: define { ptr addrspace(8), i32 } @addrspacecast_undef +; CHECK-SAME: () #[[ATTR0]] { +; CHECK-NEXT: ret { ptr addrspace(8), i32 } undef +; + %ret = addrspacecast ptr undef to ptr addrspace(7) + ret ptr addrspace(7) %ret +} + +define <2 x ptr addrspace(7)> @addrspacecast_undef_vec() { +; CHECK-LABEL: define { <2 x ptr addrspace(8)>, <2 x i32> } @addrspacecast_undef_vec +; CHECK-SAME: () #[[ATTR0]] { +; CHECK-NEXT: ret { <2 x ptr addrspace(8)>, <2 x i32> } undef +; + %ret = addrspacecast <2 x ptr> undef to <2 x ptr addrspace(7)> + ret <2 x ptr addrspace(7)> %ret +} + +define ptr addrspace(7) @addrspacecast_poison() { +; CHECK-LABEL: define { ptr addrspace(8), i32 } @addrspacecast_poison +; CHECK-SAME: () #[[ATTR0]] { +; CHECK-NEXT: ret { ptr addrspace(8), i32 } poison +; + %ret = addrspacecast ptr poison to ptr addrspace(7) + ret ptr addrspace(7) %ret +} + +define <2 x ptr addrspace(7)> @addrspacecast_poison_vec() { +; CHECK-LABEL: define { <2 x ptr addrspace(8)>, <2 x i32> } @addrspacecast_poison_vec +; CHECK-SAME: () #[[ATTR0]] { +; CHECK-NEXT: ret { <2 x ptr addrspace(8)>, <2 x i32> } poison +; + %ret = addrspacecast <2 x ptr> poison to <2 x ptr addrspace(7)> + ret <2 x ptr addrspace(7)> %ret +} + declare ptr addrspace(7) @llvm.amdgcn.make.buffer.rsrc.p7.p1(ptr addrspace(1), i16, i32, i32) define ptr addrspace(7) @make_buffer_rsrc(ptr addrspace(1) %buf, i16 %stride, i32 %numRecords, i32 %flags) {