[Bug target/84902] [8 Regression ]549.fotonik3d_r from SPEC2017 fails verification with -Ofast -march=native on Zen since r258518

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84902

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
Assembly diff in between the revisions is:

--- /tmp/good.txt       2018-03-16 15:31:17.391278644 +0100
+++ /tmp/bad.txt        2018-03-16 15:23:44.678197462 +0100
@@ -279,20 +279,10 @@
   4015ae:      66 90                   xchg   %ax,%ax

 00000000004015b0 <set_fast_math>:
-    return;
-
-  if (edx & bit_SSE)
-    set_fast_math_sse (edx);
-#else
-  unsigned int mxcsr = __builtin_ia32_stmxcsr ();
   4015b0:      0f ae 5c 24 fc          stmxcsr -0x4(%rsp)
-  mxcsr |= MXCSR_DAZ | MXCSR_FTZ;
-  __builtin_ia32_ldmxcsr (mxcsr);
   4015b5:      81 4c 24 fc 40 80 00    orl    $0x8040,-0x4(%rsp)
   4015bc:      00 
   4015bd:      0f ae 54 24 fc          ldmxcsr -0x4(%rsp)
-#endif
-}
   4015c2:      c3                      retq   
   4015c3:      66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
   4015ca:      00 00 00