<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clip

The root cause is the translation of <div class="snippet-clipboard-content notrans

Also sitofp i8 to float <div class="snippet-clipboard-content notranslate position

Signed char extraction fails to take sign into account about clspv HOT 5 OPEN

google commented on May 22, 2024

Signed char extraction fails to take sign into account

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Comments (5)

dneto0 commented on May 22, 2024

The root cause is the translation of

  %conv = sext i8 %1 to i32

The i8 is mapped to a SPIR-V 32-bit unsigned int. But the conversion of the SExt doesn't take that into account.

Original OpenCL C:

kernel void bar(global int* A, global char4* B) {
  *A = B->y;
}

last LLVM:

  %0 = load <4 x i8>, <4 x i8> addrspace(1)* %B, align 4
  %1 = extractelement <4 x i8> %0, i32 1
  %conv = sext i8 %1 to i32
  store i32 %conv, i32 addrspace(1)* %A, align 4

becomes SPIR-V:

         %28 = OpLoad %uint %27
         %29 = OpShiftRightLogical %uint %28 %uint_8
         %30 = OpBitwiseAnd %uint %29 %uint_255
         %31 = OpSConvert %uint %29   ; Not right because source type is too wide in SPIR-V
               OpStore %26 %31

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dneto0 commented on May 22, 2024

There's a corresponding problem with unsigned char.

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dneto0 commented on May 22, 2024

Also sitofp i8 to float

kernel void bar(global float* A, global char4* B) {
  *A = (float)(B->y);
}

Final LLVM:

  %1 = extractelement <4 x i8> %0, i32 1
  %conv = sitofp i8 %1 to float
  store float %conv, float addrspace(1)* %A, align 4

becomes SPIR-V:

         %29 = OpLoad %uint %28
         %30 = OpShiftRightLogical %uint %29 %uint_8
         %31 = OpBitwiseAnd %uint %30 %uint_255
         %32 = OpConvertSToF %float %30

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dneto0 commented on May 22, 2024

I can't reproduce a problem with unsigned char.

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