On Sunday, September 20, 2015 11:11:15 AM Matt Turner wrote: > On Sun, Sep 20, 2015 at 8:48 AM, Antia Puentes <apuen...@igalia.com> wrote: > > Math operations in SandyBridge do not support source swizzling > > I can't find any documentation to support this claim, but I remember > that SNB math must be in align1 mode so it can't do swizzles or > writemasking (see commit e14cc504). > > But, the documentation actually says "The supported regioning modes > for math instruction are align16, align1 with the following > restrictions: ..." > > Would be nice if we could actually find a PRM citation.
I can't find a PRM citation that mentions swizzles explicitly. However, the "Src Mod" box is unchecked, indicating that the MATH instruction can't handle source modifiers. vec4_visitor::fix_math_operand's comments interpret that as abs, negate, /and/ swizzles. Which sort of makes sense. In the internal docs, I see [reformatting mine]: "[DevSNB], [DevIVB], [DevHSW]: The supported regioning mode for math instruction is align1 with the following restrictions: * Scalar source is supported. * Source and destination horizontal stride must be 1. * Width must be the same as execution size. * Source and destination offset must be the same, except the case * of scalar source. * The math instruction does not support indirect addressing modes" (Those comments are also in the Haswell PRM.) vs. "[DevBDW]: The supported regioning mode for math instruction is align1 and align16. The following restrictions apply for align1 mode: * Scalar source is supported. * Source and destination horizontal stride must be the same. * Regioning must ensure Src.Vstride = Src.Width * Src.Hstride * Source and destination offset must be the same, except the case of scalar source." Unfortunately, I couldn't find the above "it must be align1" comments in any of the PRMs until Haswell. I assume it just got lost.
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