i386: Fix ix86_fold_builtin shift folding [PR93418]

The following testcase is miscompiled, because the variable shift left
operand, { -1, -1, -1, -1 } is represented as a VECTOR_CST with
VECTOR_CST_NPATTERNS 1 and VECTOR_CST_NELTS_PER_PATTERN 1, so when
we call builder.new_unary_operation, builder.encoded_nelts () will be just 1
and thus we encode the resulting vector as if all the elements were the
same.
For non-masked is_vshift, we could perhaps call builder.new_binary_operation
(TREE_TYPE (args[0]), args[0], args[1], false), but then there are masked
shifts, for non-is_vshift we could perhaps call it too but with args[2]
instead of args[1], but there is no builder.new_ternary_operation.
All this stuff is primarily for aarch64 anyway, on x86 we don't have any
variable length vectors, and it is not a big deal to compute all elements
and just let builder.finalize () find the most efficient VECTOR_CST
representation of the vector.  So, instead of doing too much, this just
keeps using new_unary_operation only if only one VECTOR_CST is involved
(i.e. non-masked shift by constant) and for the rest just compute all elts.

2020-01-28  Jakub Jelinek  <jakub@redhat.com>

	PR target/93418
	* config/i386/i386.c (ix86_fold_builtin) <do_shift>: If mask is not
	-1 or is_vshift is true, use new_vector with number of elts npatterns
	rather than new_unary_operation.

	* gcc.target/i386/avx2-pr93418.c: New test.

4 files changed, 35 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6db98ed..3489428 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,10 @@
 2020-01-28  Jakub Jelinek  <jakub@redhat.com>
 
+	PR target/93418
+	* config/i386/i386.c (ix86_fold_builtin) <do_shift>: If mask is not
+	-1 or is_vshift is true, use new_vector with number of elts npatterns
+	rather than new_unary_operation.
+
 	PR tree-optimization/93454
 	* gimple-fold.c (fold_array_ctor_reference): Perform
 	elt_size.to_uhwi () just once, instead of calling it in every
diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index ffe60ba..ffda3e8 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -17278,8 +17278,13 @@ ix86_fold_builtin (tree fndecl, int n_args,
 		    countt = build_int_cst (integer_type_node, count);
 		}
 	      tree_vector_builder builder;
-	      builder.new_unary_operation (TREE_TYPE (args[0]), args[0],
-					   false);
+	      if (mask != HOST_WIDE_INT_M1U || is_vshift)
+		builder.new_vector (TREE_TYPE (args[0]),
+				    TYPE_VECTOR_SUBPARTS (TREE_TYPE (args[0])),
+				    1);
+	      else
+		builder.new_unary_operation (TREE_TYPE (args[0]), args[0],
+					     false);
 	      unsigned int cnt = builder.encoded_nelts ();
 	      for (unsigned int i = 0; i < cnt; ++i)
 		{
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 44d8e67..6518f7f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2020-01-28  Jakub Jelinek  <jakub@redhat.com>
 
+	PR target/93418
+	* gcc.target/i386/avx2-pr93418.c: New test.
+
 	PR tree-optimization/93454
 	* gcc.dg/pr93454.c: New test.
 
diff --git a/gcc/testsuite/gcc.target/i386/avx2-pr93418.c b/gcc/testsuite/gcc.target/i386/avx2-pr93418.c
new file mode 100644
index 0000000..67ed33d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/avx2-pr93418.c
@@ -0,0 +1,20 @@
+/* PR target/93418 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -mavx2 -fdump-tree-optimized" } */
+/* { dg-final { scan-tree-dump-not "link_error" "optimized" } } */
+
+#include <x86intrin.h>
+
+void link_error (void);
+
+void
+foo (void)
+{
+  __m128i a = _mm_set1_epi32 (0xffffffffU);
+  __m128i b = _mm_setr_epi32 (16, 31, -34, 3);
+  __m128i c = _mm_sllv_epi32 (a, b);
+  __v4su d = (__v4su) c;
+  if (d[0] != 0xffff0000U || d[1] != 0x80000000U
+      || d[2] != 0 || d[3] != 0xfffffff8U)
+    link_error ();
+}