[llvm] [SPIR-V] Use `OpImageFetch` instead of `OpImageRead` when loading from read-only `Buffer` resource. (PR #163626)
Lucie Choi via llvm-commits
llvm-commits at lists.llvm.org
Thu Oct 16 10:49:26 PDT 2025
https://github.com/luciechoi updated https://github.com/llvm/llvm-project/pull/163626
>From 89f3e9241cff01011559e3657d5daaf14d1626ae Mon Sep 17 00:00:00 2001
From: luciechoi <ychoi0407 at gmail.com>
Date: Wed, 15 Oct 2025 20:27:15 +0000
Subject: [PATCH 1/2] [SPIR-V] Use OpImageFetch instruction when loading from
read-only buffer resource.
---
.../Target/SPIRV/SPIRVInstructionSelector.cpp | 49 +++++++++++--------
.../SPIRV/hlsl-resources/TypedBufferLoad.ll | 36 ++++++++++++++
2 files changed, 64 insertions(+), 21 deletions(-)
create mode 100644 llvm/test/CodeGen/SPIRV/hlsl-resources/TypedBufferLoad.ll
diff --git a/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp b/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp
index 989950fb8f8b5..d9a4619f3da90 100644
--- a/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp
@@ -352,9 +352,9 @@ class SPIRVInstructionSelector : public InstructionSelector {
SPIRVType *widenTypeToVec4(const SPIRVType *Type, MachineInstr &I) const;
bool extractSubvector(Register &ResVReg, const SPIRVType *ResType,
Register &ReadReg, MachineInstr &InsertionPoint) const;
- bool generateImageRead(Register &ResVReg, const SPIRVType *ResType,
- Register ImageReg, Register IdxReg, DebugLoc Loc,
- MachineInstr &Pos) const;
+ bool generateImageReadOrFetch(Register &ResVReg, const SPIRVType *ResType,
+ Register ImageReg, Register IdxReg,
+ DebugLoc Loc, MachineInstr &Pos) const;
bool BuildCOPY(Register DestReg, Register SrcReg, MachineInstr &I) const;
bool loadVec3BuiltinInputID(SPIRV::BuiltIn::BuiltIn BuiltInValue,
Register ResVReg, const SPIRVType *ResType,
@@ -1317,8 +1317,8 @@ bool SPIRVInstructionSelector::selectLoad(Register ResVReg,
}
Register IdxReg = IntPtrDef->getOperand(3).getReg();
- return generateImageRead(ResVReg, ResType, NewHandleReg, IdxReg,
- I.getDebugLoc(), I);
+ return generateImageReadOrFetch(ResVReg, ResType, NewHandleReg, IdxReg,
+ I.getDebugLoc(), I);
}
}
@@ -3633,27 +3633,32 @@ bool SPIRVInstructionSelector::selectReadImageIntrinsic(
DebugLoc Loc = I.getDebugLoc();
MachineInstr &Pos = I;
- return generateImageRead(ResVReg, ResType, NewImageReg, IdxReg, Loc, Pos);
+ return generateImageReadOrFetch(ResVReg, ResType, NewImageReg, IdxReg, Loc,
+ Pos);
}
-bool SPIRVInstructionSelector::generateImageRead(Register &ResVReg,
- const SPIRVType *ResType,
- Register ImageReg,
- Register IdxReg, DebugLoc Loc,
- MachineInstr &Pos) const {
+bool SPIRVInstructionSelector::generateImageReadOrFetch(
+ Register &ResVReg, const SPIRVType *ResType, Register ImageReg,
+ Register IdxReg, DebugLoc Loc, MachineInstr &Pos) const {
SPIRVType *ImageType = GR.getSPIRVTypeForVReg(ImageReg);
assert(ImageType && ImageType->getOpcode() == SPIRV::OpTypeImage &&
"ImageReg is not an image type.");
+
bool IsSignedInteger =
sampledTypeIsSignedInteger(GR.getTypeForSPIRVType(ImageType));
+ // Check if the "sampled" operand of the image type is 2.
+ auto SampledOp = ImageType->getOperand(6);
+ bool IsFetch = (SampledOp.getImm() != 2);
uint64_t ResultSize = GR.getScalarOrVectorComponentCount(ResType);
if (ResultSize == 4) {
- auto BMI = BuildMI(*Pos.getParent(), Pos, Loc, TII.get(SPIRV::OpImageRead))
- .addDef(ResVReg)
- .addUse(GR.getSPIRVTypeID(ResType))
- .addUse(ImageReg)
- .addUse(IdxReg);
+ auto BMI =
+ BuildMI(*Pos.getParent(), Pos, Loc,
+ TII.get(IsFetch ? SPIRV::OpImageFetch : SPIRV::OpImageRead))
+ .addDef(ResVReg)
+ .addUse(GR.getSPIRVTypeID(ResType))
+ .addUse(ImageReg)
+ .addUse(IdxReg);
if (IsSignedInteger)
BMI.addImm(0x1000); // SignExtend
@@ -3662,11 +3667,13 @@ bool SPIRVInstructionSelector::generateImageRead(Register &ResVReg,
SPIRVType *ReadType = widenTypeToVec4(ResType, Pos);
Register ReadReg = MRI->createVirtualRegister(GR.getRegClass(ReadType));
- auto BMI = BuildMI(*Pos.getParent(), Pos, Loc, TII.get(SPIRV::OpImageRead))
- .addDef(ReadReg)
- .addUse(GR.getSPIRVTypeID(ReadType))
- .addUse(ImageReg)
- .addUse(IdxReg);
+ auto BMI =
+ BuildMI(*Pos.getParent(), Pos, Loc,
+ TII.get(IsFetch ? SPIRV::OpImageFetch : SPIRV::OpImageRead))
+ .addDef(ReadReg)
+ .addUse(GR.getSPIRVTypeID(ReadType))
+ .addUse(ImageReg)
+ .addUse(IdxReg);
if (IsSignedInteger)
BMI.addImm(0x1000); // SignExtend
bool Succeed = BMI.constrainAllUses(TII, TRI, RBI);
diff --git a/llvm/test/CodeGen/SPIRV/hlsl-resources/TypedBufferLoad.ll b/llvm/test/CodeGen/SPIRV/hlsl-resources/TypedBufferLoad.ll
new file mode 100644
index 0000000000000..cbb9d11e406b5
--- /dev/null
+++ b/llvm/test/CodeGen/SPIRV/hlsl-resources/TypedBufferLoad.ll
@@ -0,0 +1,36 @@
+; RUN: llc -O0 -verify-machineinstrs -mtriple=spirv1.6-unknown-vulkan1.3-compute %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv1.6-unknown-vulkan1.3-compute %s -o - -filetype=obj | spirv-val %}
+
+; When accessing read-only `Buffer` types, SPIR-V should use `OpImageFetch` instead of `OpImageRead`.
+; https://github.com/llvm/llvm-project/issues/162891
+
+; CHECK-DAG: OpCapability SampledBuffer
+; CHECK-DAG: OpCapability ImageBuffer
+; CHECK-DAG: [[TypeInt:%[0-9]+]] = OpTypeInt 32 0
+; CHECK-DAG: [[TypeImageBuffer:%[0-9]+]] = OpTypeImage [[TypeInt]] Buffer 2 0 0 1 Unknown
+; CHECK-DAG: [[TypePtrImageBuffer:%[0-9]+]] = OpTypePointer UniformConstant [[TypeImageBuffer]]
+; CHECK-DAG: [[TypeVector:%[0-9]+]] = OpTypeVector [[TypeInt]] 4
+; CHECK-DAG: [[Index:%[0-9]+]] = OpConstant [[TypeInt]] 98
+; CHECK-DAG: [[Variable:%[0-9]+]] = OpVariable [[TypePtrImageBuffer]] UniformConstant
+ at .str = private unnamed_addr constant [7 x i8] c"rwbuff\00", align 1
+ at .str.2 = private unnamed_addr constant [5 x i8] c"buff\00", align 1
+
+define void @main() local_unnamed_addr #0 {
+entry:
+ %0 = tail call target("spirv.Image", i32, 5, 2, 0, 0, 2, 33) @llvm.spv.resource.handlefromimplicitbinding.tspirv.Image_i32_5_2_0_0_2_33t(i32 0, i32 0, i32 1, i32 0, ptr nonnull @.str)
+ %1 = tail call target("spirv.Image", i32, 5, 2, 0, 0, 1, 0) @llvm.spv.resource.handlefromimplicitbinding.tspirv.Image_i32_5_2_0_0_1_0t(i32 1, i32 0, i32 1, i32 0, ptr nonnull @.str.2)
+ %2 = tail call noundef align 4 dereferenceable(4) ptr addrspace(11) @llvm.spv.resource.getpointer.p11.tspirv.Image_i32_5_2_0_0_1_0t(target("spirv.Image", i32, 5, 2, 0, 0, 1, 0) %1, i32 98)
+; CHECK: [[Load:%[0-9]+]] = OpLoad [[TypeImageBuffer]] [[Variable]]
+; CHECK: [[ImageFetch:%[0-9]+]] = OpImageFetch [[TypeVector]] [[Load]] [[Index]]
+; CHECK: {{.*}} = OpCompositeExtract [[TypeInt]] [[ImageFetch]] 0
+ %3 = load i32, ptr addrspace(11) %2, align 4
+ %4 = tail call noundef align 4 dereferenceable(4) ptr addrspace(11) @llvm.spv.resource.getpointer.p11.tspirv.Image_i32_5_2_0_0_2_33t(target("spirv.Image", i32, 5, 2, 0, 0, 2, 33) %0, i32 99)
+ store i32 %3, ptr addrspace(11) %4, align 4
+ %5 = tail call noundef align 4 dereferenceable(4) ptr addrspace(11) @llvm.spv.resource.getpointer.p11.tspirv.Image_i32_5_2_0_0_2_33t(target("spirv.Image", i32, 5, 2, 0, 0, 2, 33) %0, i32 96)
+; CHECK: {{%[0-9]+}} = OpLoad {{.*}}
+; CHECK: {{%[0-9]+}} = OpImageRead {{.*}}
+ %6 = load i32, ptr addrspace(11) %5, align 4
+ %7 = tail call noundef align 4 dereferenceable(4) ptr addrspace(11) @llvm.spv.resource.getpointer.p11.tspirv.Image_i32_5_2_0_0_2_33t(target("spirv.Image", i32, 5, 2, 0, 0, 2, 33) %0, i32 97)
+ store i32 %6, ptr addrspace(11) %7, align 4
+ ret void
+}
>From 9a8a2f1ad3ca2fc6d11b25280023833b86d263a5 Mon Sep 17 00:00:00 2001
From: luciechoi <ychoi0407 at gmail.com>
Date: Thu, 16 Oct 2025 17:49:05 +0000
Subject: [PATCH 2/2] Flip the condition
---
llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp b/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp
index d9a4619f3da90..42c0b78956ad2 100644
--- a/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp
+++ b/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp
@@ -3646,9 +3646,10 @@ bool SPIRVInstructionSelector::generateImageReadOrFetch(
bool IsSignedInteger =
sampledTypeIsSignedInteger(GR.getTypeForSPIRVType(ImageType));
- // Check if the "sampled" operand of the image type is 2.
+ // Check if the "sampled" operand of the image type is 1.
+ // https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#OpImageFetch
auto SampledOp = ImageType->getOperand(6);
- bool IsFetch = (SampledOp.getImm() != 2);
+ bool IsFetch = (SampledOp.getImm() == 1);
uint64_t ResultSize = GR.getScalarOrVectorComponentCount(ResType);
if (ResultSize == 4) {
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