[Bug middle-end/60418] [4.9 Regression] 435.gromacs in SPEC CPU 2006 is miscompiled

["hjl.tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60418

--- Comment #14 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Richard Biener from comment #13)
> 
> Huh, adding a pre-header should _never_ do sth like that.  Can you produce
> a small testcase that exhibits these kind of changes with adding/removing
> a preheader?

I don't have a small testcase and it only shows up with -mx32.  Here
is what I see.  The diffs in 064t.copyprop3 are

diff -up good/gromacs.x.064t.copyprop3 bad/gromacs.x.064t.copyprop3
--- good/gromacs.x.064t.copyprop3    2014-03-06 13:14:22.897298915 -0800
+++ bad/gromacs.x.064t.copyprop3    2014-03-06 13:22:00.221999369 -0800
@@ -22774,6 +22774,7 @@ inl3300 (int & restrict nri, int[0:] * r
     goto <bb 8>;

   <bb 3>:
+  n_213 = 1;

   <bb 4>:
   # n_8 = PHI <1(3), n_218(7)>

n_213 is unused.  There are many diffs in SSA_NAME_VERSION in 066t.vrp1.
Diffs in 082t.reassoc1 are

diff -up good/gromacs.x.082t.reassoc1 bad/gromacs.x.082t.reassoc1
--- good/gromacs.x.082t.reassoc1    2014-03-06 13:14:22.948297990 -0800
+++ bad/gromacs.x.082t.reassoc1    2014-03-06 13:22:00.273998425 -0800
@@ -24250,11 +24250,11 @@ inl3300 (int & restrict nri, int[0:] * r
   float _201;
   float _202;
   int _206;
+  float _208;
   float _210;
   float _211;
   float _215;
   float _216;
-  float _242;

   <bb 2>:
   _19 = *nri_18(D);
@@ -24403,8 +24403,8 @@ inl3300 (int & restrict nri, int[0:] * r
   ff_152 = _155 + fp_147;
   vnb12_153 = vv_149 * c12_116;
   fijr_154 = ff_152 * c12_116;
-  _242 = vnb12_153 + vnb6_134;
-  vnbtot_156 = _242 + vnbtot_11;
+  _208 = vnb12_153 + vnb6_134;
+  vnbtot_156 = _208 + vnbtot_11;
   _157 = fijd_135 + fijc_109;
   _158 = _157 + fijr_154;
   _159 = ((_158));

When it gets to 089t.sincos, diffs are

diff -up good/gromacs.x.089t.sincos bad/gromacs.x.089t.sincos
--- good/gromacs.x.089t.sincos    2014-03-06 13:14:22.967297646 -0800
+++ bad/gromacs.x.089t.sincos    2014-03-06 13:22:00.291998098 -0800
@@ -24252,14 +24252,14 @@ inl3300 (int & restrict nri, int[0:] * r
   float _201;
   float _202;
   int _206;
+  float _208;
   float _210;
   float _211;
+  float powmult_213;
   float _215;
   float _216;
-  float powmult_238;
-  float powmult_240;
-  float powmult_241;
-  float _242;
+  float powmult_243;
+  float powmult_244;

powmult_xxx are created by make_temp_ssa_name (type, NULL, "powmult")
in tree-ssa-math-opts.c for

rsq11             = dx11*dx11+dy11*dy11+dz11*dz11;

Different powmult_xxx have nothing to do with each others. The orders of
powmult SSA_NAME_VERSION are different.  As the result, sort_by_operand_rank
sorts them differently and diffs in 125t.reassoc2 are

   powmult_80 = dx11_70 * dx11_70;
-  powmult_241 = dy11_71 * dy11_71;
-  powmult_240 = dz11_72 * dz11_72;
-  _699 = powmult_240 + powmult_80;
-  rsq11_77 = _699 + powmult_241;
+  powmult_213 = dy11_71 * dy11_71;
+  _75 = powmult_213 + powmult_80;
+  powmult_244 = dz11_72 * dz11_72;
+  rsq11_77 = _75 + powmult_244;

This is

rsq11             = dx11*dx11+dz11*dz11+dy11*dy11;

vs

rsq11             = dx11*dx11+dy11*dy11+dz11*dz11;

For FP operations, they may generate slightly different results.
It shows the reassoc pass is unstable, depending on FREE_SSANAMES when
make_temp_ssa_name is called.