[Mesa-dev] [PATCH] gallivm: fix saturated signed add / sub with llvm 9

[sroland at vmware.com]

From: Roland Scheidegger <sroland at vmware.com>

llvm 8 removed saturated unsigned add / sub x86 sse2 intrinsics, and
now llvm 9 removed the signed versions as well - they were proposed for
removal earlier, but the pattern to recognize those was very complex,
so it wasn't done then. However, instead of these arch-specific
intrinsics, there's now arch-independent intrinsics for saturated
add / sub, both for signed and unsigned, so use these.
They should have only advantages (work with arbitrary vector sizes,
optimal code for all archs), although I don't know how well they work
in practice for other archs (at least for x86 they do the right thing).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110454
---
 src/gallium/auxiliary/gallivm/lp_bld_arit.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
index 057c50ed278..02fb81afe51 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
@@ -555,6 +555,12 @@ lp_build_add(struct lp_build_context *bld,
         return bld->one;
 
       if (!type.floating && !type.fixed) {
+         if (HAVE_LLVM >= 0x0900) {
+            char intrin[32];
+            intrinsic = type.sign ? "llvm.sadd.sat" : "llvm.uadd.sat";
+            lp_format_intrinsic(intrin, sizeof intrin, intrinsic, bld->vec_type);
+            return lp_build_intrinsic_binary(builder, intrin, bld->vec_type, a, b);
+         }
          if (type.width * type.length == 128) {
             if (util_cpu_caps.has_sse2) {
                if (type.width == 8)
@@ -625,6 +631,7 @@ lp_build_add(struct lp_build_context *bld,
           * NOTE: cmp/select does sext/trunc of the mask. Does not seem to
           * interfere with llvm's ability to recognize the pattern but seems
           * a bit brittle.
+          * NOTE: llvm 9+ always uses (non arch specific) intrinsic.
           */
          LLVMValueRef overflowed = lp_build_cmp(bld, PIPE_FUNC_GREATER, a, res);
          res = lp_build_select(bld, overflowed,
@@ -876,6 +883,12 @@ lp_build_sub(struct lp_build_context *bld,
         return bld->zero;
 
       if (!type.floating && !type.fixed) {
+         if (HAVE_LLVM >= 0x0900) {
+            char intrin[32];
+            intrinsic = type.sign ? "llvm.ssub.sat" : "llvm.usub.sat";
+            lp_format_intrinsic(intrin, sizeof intrin, intrinsic, bld->vec_type);
+            return lp_build_intrinsic_binary(builder, intrin, bld->vec_type, a, b);
+         }
          if (type.width * type.length == 128) {
             if (util_cpu_caps.has_sse2) {
                if (type.width == 8)
@@ -925,6 +938,7 @@ lp_build_sub(struct lp_build_context *bld,
           * NOTE: cmp/select does sext/trunc of the mask. Does not seem to
           * interfere with llvm's ability to recognize the pattern but seems
           * a bit brittle.
+          * NOTE: llvm 9+ always uses (non arch specific) intrinsic.
           */
          LLVMValueRef no_ov = lp_build_cmp(bld, PIPE_FUNC_GREATER, a, b);
          a = lp_build_select(bld, no_ov, a, b);
-- 
2.17.1