ac/llvm: set !fpmath 3.0 for llvm.sqrt

LLVM will be changed to increase precision with additional instructions,
which we don't want.

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25492>

src/amd/llvm/ac_llvm_build.c

@@ -100,12 +100,15 @@ void ac_llvm_context_init(struct ac_llvm_context *ctx, struct ac_llvm_compiler *
    ctx->i1true = LLVMConstInt(ctx->i1, 1, false);
 
    ctx->range_md_kind = LLVMGetMDKindIDInContext(ctx->context, "range", 5);
-
    ctx->invariant_load_md_kind = LLVMGetMDKindIDInContext(ctx->context, "invariant.load", 14);
-
    ctx->uniform_md_kind = LLVMGetMDKindIDInContext(ctx->context, "amdgpu.uniform", 14);
+   ctx->fpmath_md_kind = LLVMGetMDKindIDInContext(ctx->context, "fpmath", 6);
 
    ctx->empty_md = LLVMMDNodeInContext(ctx->context, NULL, 0);
+
+   LLVMValueRef three = LLVMConstReal(ctx->f32, 3);
+   ctx->three_md = LLVMMDNodeInContext(ctx->context, &three, 1);
+
    ctx->flow = calloc(1, sizeof(*ctx->flow));
 
    ctx->ring_offsets_index = INT32_MAX;

src/amd/llvm/ac_llvm_build.h

@@ -121,7 +121,9 @@ struct ac_llvm_context {
    unsigned range_md_kind;
    unsigned invariant_load_md_kind;
    unsigned uniform_md_kind;
+   unsigned fpmath_md_kind;
    LLVMValueRef empty_md;
+   LLVMValueRef three_md;
 
    const struct radeon_info *info;
    enum amd_gfx_level gfx_level;

src/amd/llvm/ac_nir_to_llvm.c

@@ -801,6 +801,7 @@ static bool visit_alu(struct ac_nir_context *ctx, const nir_alu_instr *instr)
    case nir_op_fsqrt:
       result =
          emit_intrin_1f_param(&ctx->ac, "llvm.sqrt", ac_to_float_type(&ctx->ac, def_type), src[0]);
+      LLVMSetMetadata(result, ctx->ac.fpmath_md_kind, ctx->ac.three_md);
       break;
    case nir_op_fexp2:
       result =