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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.
This commit is contained in:
Jakub Jelinek 2020-01-28 08:46:23 +01:00
parent 3c076c9642
commit bff948aa33
4 changed files with 35 additions and 2 deletions
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5
gcc/ChangeLog
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@ -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

5
gcc/config/i386/i386.c
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@ -17278,6 +17278,11 @@ ix86_fold_builtin (tree fndecl, int n_args,
countt = build_int_cst (integer_type_node, count);
}
tree_vector_builder builder;
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 ();

3
gcc/testsuite/ChangeLog
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@ -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.

20
gcc/testsuite/gcc.target/i386/avx2-pr93418.c Normal file
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@ -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 ();
}