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Split FindUMsb64 into two 32bit ops

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This commit is contained in:
Marcin Mikołajczyk 2025-06-05 21:36:44 +01:00
parent 353f425942
commit c539c0d7fc
2 changed files with 12 additions and 2 deletions
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12
src/shader_recompiler/backend/spirv/emit_spirv_integer.cpp
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@ -230,7 +230,17 @@ Id EmitFindUMsb32(EmitContext& ctx, Id value) {
}
Id EmitFindUMsb64(EmitContext& ctx, Id value) {
return ctx.OpFindUMsb(ctx.U64, value);
// Vulkan restricts some bitwise operations to 32-bit only, so decompose into
// two 32-bit values and select the correct result.
const Id unpacked{ctx.OpBitcast(ctx.U32[2], value)};
const Id hi{ctx.OpCompositeExtract(ctx.U32[1], unpacked, 1U)};
const Id lo{ctx.OpCompositeExtract(ctx.U32[1], unpacked, 0U)};
const Id hi_msb{ctx.OpFindUMsb(ctx.U32[1], hi)};
const Id lo_msb{ctx.OpFindUMsb(ctx.U32[1], lo)};
const Id found_hi{ctx.OpINotEqual(ctx.U1[1], hi_msb, ctx.ConstU32(u32(-1)))};
const Id shifted_hi{ctx.OpIAdd(ctx.U32[1], hi_msb, ctx.ConstU32(32u))};
// value == 0 case is checked in IREmitter
return ctx.OpSelect(ctx.U32[1], found_hi, shifted_hi, lo_msb);
}
Id EmitFindILsb32(EmitContext& ctx, Id value) {

2
src/shader_recompiler/frontend/translate/scalar_alu.cpp
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@ -695,7 +695,7 @@ void Translator::S_FLBIT_I32_B64(const GcnInst& inst) {
const IR::U32 msb_pos = ir.FindUMsb(src0);
const IR::U32 pos_from_left = ir.ISub(ir.Imm32(63), msb_pos);
// Select 0xFFFFFFFF if src0 was 0
const IR::U1 cond = ir.INotEqual(src0, ir.Imm32(0));
const IR::U1 cond = ir.INotEqual(src0, ir.Imm64(u64(0u)));
SetDst(inst.dst[0], IR::U32{ir.Select(cond, pos_from_left, ir.Imm32(~0U))});
}