Hi!
The following testcase is miscompiled on x86_64 since PR110551 r14-4968
commit. That commit added 2 peephole2s, one for
mov imm,%rXX; mov %rYY,%rax; mulq %rXX -> mov imm,%rax; mulq %rYY
which I believe is ok, and another one for
mov imm,%rXX; mov %rYY,%rdx; mulx %rXX, %rZZ, %rWW -> mov imm,%rdx; mulx %rYY,
%rZZ, %rWW
which is wrong. Both peephole2s verify that %rXX above is dead at
the end of the pattern, by checking if %rXX is either one of the
registers overwritten in the multiplication (%rdx:%rax in the first
case, the 2 destination registers of mulx in the latter case), because
we no longer set %rXX to that immediate (we set %rax resp. %rdx to it
instead) when the peephole2 replaces it. But, we also need to ensure
that the other register previously set to the value of %rYY and newly
to imm isn't used after the multiplication, and neither of the peephole2s
does that. Now, for the first one (at least assuming in the % pattern
the matching operand (i.e. hardcoded %rax resp. %rdx) after RA will always go
first) I think it is always the case, because operands[2] if it must be %rax
register will be overwritten by mulq writing to %rdx:%rax. But in the
second case, there is no reason why %rdx couldn't be used after the pattern,
and if it is (like in the testcase), we can't make those changes.
So, the patch checks similarly to operands[0] that operands[2] (which ought
to be %rdx if RA puts the % match_dup operand first and nothing swaps it
afterwards) is either the same register as one of the destination registers
of mulx or dies at the end of the multiplication.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2023-11-16 Jakub Jelinek <ja...@redhat.com>
PR target/112526
* config/i386/i386.md
(mov imm,%rax; mov %rdi,%rdx; mulx %rax -> mov imm,%rdx; mulx %rdi):
Verify in define_peephole2 that operands[2] dies or is overwritten
at the end of multiplication.
* gcc.target/i386/bmi2-pr112526.c: New test.
--- gcc/config/i386/i386.md.jj 2023-11-14 21:38:38.667046713 +0100
+++ gcc/config/i386/i386.md 2023-11-15 17:03:28.308048728 +0100
@@ -9918,7 +9918,10 @@ (define_peephole2
&& REGNO (operands[0]) != REGNO (operands[3])
&& (REGNO (operands[0]) == REGNO (operands[4])
|| REGNO (operands[0]) == REGNO (operands[5])
- || peep2_reg_dead_p (3, operands[0]))"
+ || peep2_reg_dead_p (3, operands[0]))
+ && (REGNO (operands[2]) == REGNO (operands[4])
+ || REGNO (operands[2]) == REGNO (operands[5])
+ || peep2_reg_dead_p (3, operands[2]))"
[(set (match_dup 2) (match_dup 1))
(parallel [(set (match_dup 4)
(mult:DWIH (match_dup 2) (match_dup 3)))
--- gcc/testsuite/gcc.target/i386/bmi2-pr112526.c.jj 2023-11-15
16:58:02.230380183 +0100
+++ gcc/testsuite/gcc.target/i386/bmi2-pr112526.c 2023-11-15
17:02:22.478942259 +0100
@@ -0,0 +1,27 @@
+/* PR target/112526 */
+/* { dg-do run { target { bmi2 && int128 } } } */
+/* { dg-options "-O2 -mbmi2" } */
+
+#include "bmi2-check.h"
+
+__attribute__((noipa)) void
+foo (unsigned long x, unsigned __int128 *y, unsigned long z, unsigned long *w)
+{
+ register unsigned long a __asm ("%r10") = x + z;
+ register unsigned __int128 b __asm ("%r8") = ((unsigned __int128) a) *
257342423UL;
+ asm volatile ("" : "+r" (b));
+ asm volatile ("" : "+d" (a));
+ *y = b;
+ *w = a;
+}
+
+static void
+bmi2_test ()
+{
+ unsigned __int128 y;
+ unsigned long w;
+ foo (10268318293806702989UL, &y, 4702524958196331333UL, &w);
+ if (y != ((((unsigned __int128) 0xc72d2c9UL) << 64) | 0x9586adfdc95b225eUL)
+ || w != 14970843252003034322UL)
+ abort ();
+}
Jakub
