Lower OpenCL mix builtin to arithmetic operations - #1655
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The OpenCL C specification defines mix(x, y, a) as x + (y - x) * a. Previously, clspv mapped mix directly to the GLSL extended instruction FMix, which evaluates x * (1 - a) + y * a. Due to floating-point rounding differences, this can fail OpenCL CTS accuracy requirements. Lower mix in ReplaceOpenCLBuiltinPass into explicit FSub, FMul, and FAdd operations conforming to the OpenCL specification formula, unless --use-native-builtins=mix or -native-math is requested. When the first operand is a vector and the third operand is scalar, splat the scalar argument across the vector lanes. Update existing mix lit tests to use --use-native-builtins=mix to continue validating FMix instruction generation, and add tests covering lowered scalar and vector mix.
alan-baker
approved these changes
Sep 25, 2026
rjodinchr
enabled auto-merge (squash)
September 25, 2026 14:13
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The OpenCL C specification defines mix(x, y, a) as x + (y - x) * a. Previously, clspv mapped mix directly to the GLSL extended instruction FMix, which evaluates x * (1 - a) + y * a. Due to floating-point rounding differences, this can fail OpenCL CTS accuracy requirements.
Lower mix in ReplaceOpenCLBuiltinPass into explicit FSub, FMul, and FAdd operations conforming to the OpenCL specification formula, unless --use-native-builtins=mix or -native-math is requested. When the first operand is a vector and the third operand is scalar, splat the scalar argument across the vector lanes.
Update existing mix lit tests to use --use-native-builtins=mix to continue validating FMix instruction generation, and add tests covering lowered scalar and vector mix.