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* [gcc(refs/vendors/redhat/heads/gcc-8-branch)] optabs: Don't reuse target for multi-word expansions if it overlaps operand(s) [PR97073]
@ 2020-09-28 9:16 Jakub Jelinek
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From: Jakub Jelinek @ 2020-09-28 9:16 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:e5438c920c4d6ffad6eb85640698f4ff0307c0d7
commit e5438c920c4d6ffad6eb85640698f4ff0307c0d7
Author: Jakub Jelinek <jakub@redhat.com>
Date: Sun Sep 27 23:18:26 2020 +0200
optabs: Don't reuse target for multi-word expansions if it overlaps operand(s) [PR97073]
The following testcase is miscompiled on i686-linux, because
we try to expand a double-word bitwise logic operation with op0
being a (mem:DI u) and target (mem:DI u+4), i.e. partial overlap, and
thus end up with:
movl 4(%esp), %eax
andl u, %eax
movl %eax, u+4
! movl u+4, %eax optimized out
andl 8(%esp), %eax
movl %eax, u+8
rather than with the desired:
movl 4(%esp), %edx
movl 8(%esp), %eax
andl u, %edx
andl u+4, %eax
movl %eax, u+8
movl %edx, u+4
because the store of the first word to target overwrites the second word of
the operand.
expand_binop for this (and several similar places) already check for target
== op0 or target == op1, this patch just adds reg_overlap_mentioned_p calls
next to it.
Pedantically, at least for some of these it might be sufficient to force
a different target if there is overlap but target is not rtx_equal_p to
the operand (e.g. in this bitwise logical case, but e.g. not in the shift
cases where there is reordering), though that would go against the
preexisting target == op? checks and the rationale that REG_EQUAL notes in
that case isn't correct.
2020-09-27 Jakub Jelinek <jakub@redhat.com>
PR middle-end/97073
* optabs.c (expand_binop, expand_absneg_bit, expand_unop,
expand_copysign_bit): Check reg_overlap_mentioned_p between target
and operand(s) and if it returns true, force a pseudo as target.
* gcc.c-torture/execute/pr97073.c: New test.
(cherry picked from commit a4b31d5807f2bc67c8999b3d53369cf2a5c6e1ec)
Diff:
---
gcc/optabs.c | 14 +++++++++++++-
gcc/testsuite/gcc.c-torture/execute/pr97073.c | 21 +++++++++++++++++++++
2 files changed, 34 insertions(+), 1 deletion(-)
diff --git a/gcc/optabs.c b/gcc/optabs.c
index 51d838d4f93..9e93097fa55 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -1363,6 +1363,8 @@ expand_binop (machine_mode mode, optab binoptab, rtx op0, rtx op1,
if (target == 0
|| target == op0
|| target == op1
+ || reg_overlap_mentioned_p (target, op0)
+ || reg_overlap_mentioned_p (target, op1)
|| !valid_multiword_target_p (target))
target = gen_reg_rtx (int_mode);
@@ -1437,6 +1439,8 @@ expand_binop (machine_mode mode, optab binoptab, rtx op0, rtx op1,
if (target == 0
|| target == op0
|| target == op1
+ || reg_overlap_mentioned_p (target, op0)
+ || reg_overlap_mentioned_p (target, op1)
|| !valid_multiword_target_p (target))
target = gen_reg_rtx (int_mode);
@@ -1495,6 +1499,8 @@ expand_binop (machine_mode mode, optab binoptab, rtx op0, rtx op1,
|| target == op0
|| target == op1
|| !REG_P (target)
+ || reg_overlap_mentioned_p (target, op0)
+ || reg_overlap_mentioned_p (target, op1)
|| !valid_multiword_target_p (target))
target = gen_reg_rtx (int_mode);
@@ -2632,6 +2638,7 @@ expand_absneg_bit (enum rtx_code code, scalar_float_mode mode,
if (target == 0
|| target == op0
+ || reg_overlap_mentioned_p (target, op0)
|| (nwords > 1 && !valid_multiword_target_p (target)))
target = gen_reg_rtx (mode);
@@ -2910,7 +2917,10 @@ expand_unop (machine_mode mode, optab unoptab, rtx op0, rtx target,
int i;
rtx_insn *insns;
- if (target == 0 || target == op0 || !valid_multiword_target_p (target))
+ if (target == 0
+ || target == op0
+ || reg_overlap_mentioned_p (target, op0)
+ || !valid_multiword_target_p (target))
target = gen_reg_rtx (int_mode);
start_sequence ();
@@ -3420,6 +3430,8 @@ expand_copysign_bit (scalar_float_mode mode, rtx op0, rtx op1, rtx target,
if (target == 0
|| target == op0
|| target == op1
+ || reg_overlap_mentioned_p (target, op0)
+ || reg_overlap_mentioned_p (target, op1)
|| (nwords > 1 && !valid_multiword_target_p (target)))
target = gen_reg_rtx (mode);
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr97073.c b/gcc/testsuite/gcc.c-torture/execute/pr97073.c
new file mode 100644
index 00000000000..1955e6b8bd2
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr97073.c
@@ -0,0 +1,21 @@
+/* PR middle-end/97073 */
+/* { dg-additional-options "-mno-stv" { target i?86-*-* x86_64-*-* } } */
+
+typedef unsigned long long L;
+union U { L i; struct T { unsigned k; L l; } j; } u;
+
+__attribute__((noinline,noclone)) void
+foo (L x)
+{
+ u.j.l = u.i & x;
+}
+
+int
+main ()
+{
+ u.i = 5;
+ foo (-1ULL);
+ if (u.j.l != 5)
+ __builtin_abort ();
+ return 0;
+}
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