The testcase is miscompiled to this:
...
movl (%rsi), %ecx
cmpl %ecx, (%rdi)
sbbl %edx, %edx
cmovbe %edx, %eax
ret
but sbbl only preserves the carry flag, not the zero flag. I suppose
one could use different patterns with different CC modes, but this is
the safest fix.
Bootstrapped/regtested x86_64-pc-linux-gnu, ok for mainline?
I also reproduced this at least on 4.7; help would be welcome on
committing it to the branches. Thanks in advance!
Paolo
2012-04-27 Paolo Bonzini <bonz...@gnu.org>
PR target/53138
* config/i386/i386.md (x86_mov<mode>cc_0_m1_neg): Add clobber.
2012-04-27 Paolo Bonzini <bonz...@gnu.org>
PR target/53138
* gcc.c-torture/execute/20120427-1.c: New testcase.
Index: config/i386/i386.md
===================================================================
--- config/i386/i386.md (revisione 186859)
+++ config/i386/i386.md (copia locale)
@@ -16439,7 +16439,8 @@
(define_insn "*x86_mov<mode>cc_0_m1_neg"
[(set (match_operand:SWI48 0 "register_operand" "=r")
(neg:SWI48 (match_operator 1 "ix86_carry_flag_operator"
- [(reg FLAGS_REG) (const_int 0)])))]
+ [(reg FLAGS_REG) (const_int 0)])))
+ (clobber (reg:CC FLAGS_REG))]
""
"sbb{<imodesuffix>}\t%0, %0"
[(set_attr "type" "alu")
Index: testsuite/gcc.c-torture/execute/20120427-1.c
===================================================================
--- testsuite/gcc.c-torture/execute/20120427-1.c (revisione 0)
+++ testsuite/gcc.c-torture/execute/20120427-1.c (revisione 0)
@@ -0,0 +1,36 @@
+typedef struct sreal
+{
+ unsigned sig; /* Significant. */
+ int exp; /* Exponent. */
+} sreal;
+
+sreal_compare (sreal *a, sreal *b)
+{
+ if (a->exp > b->exp)
+ return 1;
+ if (a->exp < b->exp)
+ return -1;
+ if (a->sig > b->sig)
+ return 1;
+ return -(a->sig < b->sig);
+}
+
+sreal a[] = {
+ { 0, 0 },
+ { 1, 0 },
+ { 0, 1 },
+ { 1, 1 }
+};
+
+int main()
+{
+ int i, j;
+ for (i = 0; i <= 3; i++) {
+ for (j = 0; j < 3; j++) {
+ if (i < j && sreal_compare(&a[i], &a[j]) != -1) abort();
+ if (i == j && sreal_compare(&a[i], &a[j]) != 0) abort();
+ if (i > j && sreal_compare(&a[i], &a[j]) != 1) abort();
+ }
+ }
+ return 0;
+}
