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[SPIR-V] Fix precision for dot2add #7861

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Merged
merged 2 commits into from
Nov 10, 2025
+35 −18
Merged

[SPIR-V] Fix precision for dot2add #7861

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e5ec194
Fix precision for .
luciechoi Oct 31, 2025
6a495e2
Multiplication happens with half precision
luciechoi Nov 1, 2025
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26 changes: 17 additions & 9 deletions tools/clang/lib/SPIRV/SpirvEmitter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13165,18 +13165,26 @@ SpirvInstruction *SpirvEmitter::processIntrinsicDP2a(const CallExpr *callExpr) {
SpirvInstruction *arg1Instr = doExpr(arg1);
SpirvInstruction *arg2Instr = doExpr(arg2);

// Create the dot product of the half2 vectors.
SpirvInstruction *dotInstr = spvBuilder.createBinaryOp(
spv::Op::OpDot, componentType, arg0Instr, arg1Instr, loc, range);
// Multiply the two half2 vectors and convert the result to float2.
SpirvInstruction *mulInstr = spvBuilder.createBinaryOp(
spv::Op::OpFMul, vecType, arg0Instr, arg1Instr, loc, range);
SpirvInstruction *convertInstr = spvBuilder.createUnaryOp(
spv::Op::OpFConvert,
astContext.getExtVectorType(astContext.FloatTy, vecSize), mulInstr, loc,
range);

// Convert dot product (half type) to result type (float).
QualType resultType = callExpr->getType();
SpirvInstruction *floatDotInstr = spvBuilder.createUnaryOp(
spv::Op::OpFConvert, resultType, dotInstr, loc, range);
// Extract each float element and and sum them up.
SpirvInstruction *extractedElem0 = spvBuilder.createCompositeExtract(
astContext.FloatTy, convertInstr, {0}, loc, range);
SpirvInstruction *extractedElem1 = spvBuilder.createCompositeExtract(
astContext.FloatTy, convertInstr, {1}, loc, range);
SpirvInstruction *dotInstr =
spvBuilder.createBinaryOp(spv::Op::OpFAdd, astContext.FloatTy,
extractedElem0, extractedElem1, loc, range);

// Sum the dot product result and accumulator and return.
return spvBuilder.createBinaryOp(spv::Op::OpFAdd, resultType, floatDotInstr,
arg2Instr, loc, range);
return spvBuilder.createBinaryOp(spv::Op::OpFAdd, astContext.FloatTy,
dotInstr, arg2Instr, loc, range);
}

SpirvInstruction *
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27 changes: 18 additions & 9 deletions tools/clang/test/CodeGenSPIRV/intrinsics.dot2add.hlsl
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Original file line number Diff line number Diff line change
Expand Up @@ -12,9 +12,12 @@ float main() : SV_Target {
// CHECK: [[input1A:%[0-9]+]] = OpLoad %v2half %input1A
// CHECK: [[input1B:%[0-9]+]] = OpLoad %v2half %input1B
// CHECK: [[acc1:%[0-9]+]] = OpLoad %float %acc1
// CHECK: [[dot1_0:%[0-9]+]] = OpDot %half [[input1A]] [[input1B]]
// CHECK: [[dot1:%[0-9]+]] = OpFConvert %float [[dot1_0]]
// CHECK: [[res1:%[0-9]+]] = OpFAdd %float [[dot1]] [[acc1]]
// CHECK: [[mult1A:%[0-9]+]] = OpFMul %v2half [[input1A]] [[input1B]]
// CHECK: [[convert1A:%[0-9]+]] = OpFConvert %v2float [[mult1A]]
// CHECK: [[extract1A_0:%[0-9]+]] = OpCompositeExtract %float [[convert1A]] 0
// CHECK: [[extract1A_1:%[0-9]+]] = OpCompositeExtract %float [[convert1A]] 1
// CHECK: [[add1A:%[0-9]+]] = OpFAdd %float [[extract1A_0]] [[extract1A_1]]
// CHECK: [[res1:%[0-9]+]] = OpFAdd %float [[add1A]] [[acc1]]
res += dot2add(input1A, input1B, acc1);

half4 input2;
Expand All @@ -25,9 +28,12 @@ float main() : SV_Target {
// CHECK: [[input2B:%[0-9]+]] = OpVectorShuffle %v2half [[input2_1]] [[input2_1]] 2 3
// CHECK: [[acc2_0:%[0-9]+]] = OpLoad %int %acc2
// CHECK: [[acc2:%[0-9]+]] = OpConvertSToF %float [[acc2_0]]
// CHECK: [[dot2_0:%[0-9]+]] = OpDot %half [[input2A]] [[input2B]]
// CHECK: [[dot2:%[0-9]+]] = OpFConvert %float [[dot2_0]]
// CHECK: [[res2:%[0-9]+]] = OpFAdd %float [[dot2]] [[acc2]]
// CHECK: [[mult2A:%[0-9]+]] = OpFMul %v2half [[input2A]] [[input2B]]
// CHECK: [[convert2A:%[0-9]+]] = OpFConvert %v2float [[mult2A]]
// CHECK: [[extract2A_0:%[0-9]+]] = OpCompositeExtract %float [[convert2A]] 0
// CHECK: [[extract2A_1:%[0-9]+]] = OpCompositeExtract %float [[convert2A]] 1
// CHECK: [[add2A:%[0-9]+]] = OpFAdd %float [[extract2A_0]] [[extract2A_1]]
// CHECK: [[res2:%[0-9]+]] = OpFAdd %float [[add2A]] [[acc2]]
res += dot2add(input2.xy, input2.zw, acc2);

float input3A;
Expand All @@ -44,9 +50,12 @@ float main() : SV_Target {
// CHECK: [[input3B:%[0-9]+]] = OpConvertSToF %v2half [[input3B_5]]
// CHECK: [[acc3_1:%[0-9]+]] = OpLoad %half %acc3
// CHECK: [[acc3:%[0-9]+]] = OpFConvert %float [[acc3_1]]
// CHECK: [[dot3_1:%[0-9]+]] = OpDot %half [[input3A]] [[input3B]]
// CHECK: [[dot3:%[0-9]+]] = OpFConvert %float [[dot3_1]]
// CHECK: [[res3:%[0-9]+]] = OpFAdd %float [[dot3]] [[acc3]]
// CHECK: [[mult3A:%[0-9]+]] = OpFMul %v2half [[input3A]] [[input3B]]
// CHECK: [[convert3A:%[0-9]+]] = OpFConvert %v2float [[mult3A]]
// CHECK: [[extract3A_0:%[0-9]+]] = OpCompositeExtract %float [[convert3A]] 0
// CHECK: [[extract3A_1:%[0-9]+]] = OpCompositeExtract %float [[convert3A]] 1
// CHECK: [[add3A:%[0-9]+]] = OpFAdd %float [[extract3A_0]] [[extract3A_1]]
// CHECK: [[res3:%[0-9]+]] = OpFAdd %float [[add3A]] [[acc3]]
res += dot2add(input3A, input3B, acc3);

return res;
Expand Down