gallivm: faster iround implementation for sse2

sse2 supports round to nearest directly (or rather, assuming default nearest
rounding mode in MXCSR). Use intrinsic to use this rather than round (sse41)
or bit manipulation whenever possible.

1 files changed, 53 insertions, 1 deletions

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
index 4f108f6e818..6ab13506e15 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
@@ -1053,6 +1053,54 @@ lp_build_round_sse41(struct lp_build_context *bld,
 }
 
 
+static INLINE LLVMValueRef
+lp_build_iround_nearest_sse2(struct lp_build_context *bld,
+                             LLVMValueRef a)
+{
+   const struct lp_type type = bld->type;
+   LLVMTypeRef i32t = LLVMInt32Type();
+   LLVMTypeRef ret_type = lp_build_int_vec_type(type);
+   const char *intrinsic;
+   LLVMValueRef res;
+
+   assert(type.floating);
+   /* using the double precision conversions is a bit more complicated */
+   assert(type.width == 32);
+
+   assert(lp_check_value(type, a));
+   assert(util_cpu_caps.has_sse2);
+
+   /* This is relying on MXCSR rounding mode, which should always be nearest. */
+   if (type.length == 1) {
+      LLVMTypeRef vec_type;
+      LLVMValueRef undef;
+      LLVMValueRef arg;
+      LLVMValueRef index0 = LLVMConstInt(i32t, 0, 0);
+
+      vec_type = LLVMVectorType(bld->elem_type, 4);
+
+      intrinsic = "llvm.x86.sse.cvtss2si";
+
+      undef = LLVMGetUndef(vec_type);
+
+      arg = LLVMBuildInsertElement(bld->builder, undef, a, index0, "");
+
+      res = lp_build_intrinsic_unary(bld->builder, intrinsic,
+                                     ret_type, arg);
+   }
+   else {
+      assert(type.width*type.length == 128);
+
+      intrinsic = "llvm.x86.sse2.cvtps2dq";
+
+      res = lp_build_intrinsic_unary(bld->builder, intrinsic,
+                                     ret_type, a);
+   }
+
+   return res;
+}
+
+
 /**
  * Return the integer part of a float (vector) value (== round toward zero).
  * The returned value is a float (vector).
@@ -1217,7 +1265,11 @@ lp_build_iround(struct lp_build_context *bld,
 
    assert(lp_check_value(type, a));
 
-   if (util_cpu_caps.has_sse4_1 &&
+   if (util_cpu_caps.has_sse2 &&
+       ((type.width == 32) && (type.length == 1 || type.length == 4))) {
+      return lp_build_iround_nearest_sse2(bld, a);
+   }
+   else if (util_cpu_caps.has_sse4_1 &&
        (type.length == 1 || type.width*type.length == 128)) {
       res = lp_build_round_sse41(bld, a, LP_BUILD_ROUND_SSE41_NEAREST);
    }