[PATCH v2] Explicitly view_convert_expr mask to signed type when folding pblendvb builtins.

[liuhongt via Gcc-patches]

> I think this is a better patch and will always be correct and still
> get folded at the gimple level (correctly):
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index d4ff56ee8dd..02bf5ba93a5 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -18561,8 +18561,10 @@ ix86_gimple_fold_builtin (gimple_stmt_iterator *gsi)
>               tree itype = GET_MODE_INNER (TYPE_MODE (type)) == E_SFmode
>                 ? intSI_type_node : intDI_type_node;
>               type = get_same_sized_vectype (itype, type);
> -             arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
>             }
> +         else
> +           type = signed_type_for (type);
> +         arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
>           tree zero_vec = build_zero_cst (type);
>           tree cmp_type = truth_type_for (type);
>           tree cmp = gimple_build (&stmts, LT_EXPR, cmp_type, arg2, zero_vec);
>
>

Yes, thanks.

Here's the updated patch:

Since mask < 0 will be always false for vector char when
-funsigned-char, but vpblendvb needs to check the most significant
bit. The patch explicitly VCE to vector signed char.


gcc/ChangeLog:

        PR target/110108
        * config/i386/i386.cc (ix86_gimple_fold_builtin): Explicitly
        view_convert_expr mask to signed type when folding pblendvb
        builtins.

gcc/testsuite/ChangeLog:

        * gcc.target/i386/pr110108-2.c: New test.
---
 gcc/config/i386/i386.cc                    |  4 +++-
 gcc/testsuite/gcc.target/i386/pr110108-2.c | 14 ++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr110108-2.c

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index da20c2c49de..4e594a9c88e 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -18561,8 +18561,10 @@ ix86_gimple_fold_builtin (gimple_stmt_iterator *gsi)
              tree itype = GET_MODE_INNER (TYPE_MODE (type)) == E_SFmode
                ? intSI_type_node : intDI_type_node;
              type = get_same_sized_vectype (itype, type);
-             arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
            }
+         else
+           type = signed_type_for (type);
+         arg2 = gimple_build (&stmts, VIEW_CONVERT_EXPR, type, arg2);
          tree zero_vec = build_zero_cst (type);
          tree cmp_type = truth_type_for (type);
          tree cmp = gimple_build (&stmts, LT_EXPR, cmp_type, arg2, zero_vec);
diff --git a/gcc/testsuite/gcc.target/i386/pr110108-2.c 
b/gcc/testsuite/gcc.target/i386/pr110108-2.c
new file mode 100644
index 00000000000..2d1d2fd4991
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr110108-2.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-mavx2 -O2 -funsigned-char" } */
+/* { dg-final { scan-assembler-times "vpblendvb" 2 } } */
+
+#include <immintrin.h>
+__m128i do_stuff_128(__m128i X0, __m128i X1, __m128i X2) {
+  __m128i Result = _mm_blendv_epi8(X0, X1, X2);
+  return Result;
+}
+
+__m256i do_stuff_256(__m256i X0, __m256i X1, __m256i X2) {
+  __m256i Result = _mm256_blendv_epi8(X0, X1, X2);
+  return Result;
+}
-- 
2.39.1.388.g2fc9e9ca3c