Change default to JIT without fma#2076
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lgritz wants to merge 1 commit intoAcademySoftwareFoundation:mainfrom
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Change default to JIT without fma#2076lgritz wants to merge 1 commit intoAcademySoftwareFoundation:mainfrom
lgritz wants to merge 1 commit intoAcademySoftwareFoundation:mainfrom
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The ShadingSystem option "llvm_jit_fma" seems to advertise that it switches between no fused multiply-add (the default, 0), versus allowing fma to be generated in the JIT. The underlying LLVM option is actually a 3-way switch about how to utilized fused ops: Strict (no fused ops), Standard (allow fma but not other fused ops), or Fast (allow other fused ops when it will speed things up). Aside: "standard" is really confusing, as one might think it means original standard IEEE 754 definitions that lacked fma. These are not the same! We were using llvm_jit_fma to switch between Standard and Fast, but upon closer examination, we now believe that it should control a switch between Strict and Standard, and Strict should be the default. This seems to directly change the pesky render-microfacet test, which has always seemed to have an unusual sensitivity to the specific processor. Hopefully, users will find that across the board, it leads to their renderers having fewer minor pixel differences from one platform to another. Signed-off-by: Larry Gritz <lg@larrygritz.com>
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The ShadingSystem option "llvm_jit_fma" seems to advertise that it switches between no fused multiply-add (the default, 0), versus allowing fma to be generated in the JIT.
The underlying LLVM option is actually a 3-way switch about how to utilize fused ops: Strict (no fused ops), Standard (allow fma but not other fused ops), or Fast (allow other fused ops when it will speed things up). Aside: "standard" is really confusing, as one might think it means original standard IEEE 754 definitions that lacked fma.
These are not the same! We were using llvm_jit_fma to switch between Standard and Fast, but upon closer examination, we now believe that it should control a switch between Strict and Standard, and Strict should be the default.
This seems to directly change the pesky render-microfacet test, which has always seemed to have an unusual sensitivity to the specific processor. Hopefully, users will find that across the board, it leads to their renderers having fewer minor pixel differences from one platform to another.