diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 80151a7ce670..f1f6e5ca7f24 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2010-01-15  Jing Yu  <jingyu@google.com>
+
+	PR rtl-optimization/42691
+	* combine.c (try_combine): Set changed_i3_dest to 1 when I2 and I3 set
+	a pseudo to a constant and are merged, and adjust comments.
+
 2010-01-15  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* config/i386/sse.md (avx_vperm2f128<mode>3): Fix typo.
diff --git a/gcc/combine.c b/gcc/combine.c
index 5ae557c180af..e5d4c5aafc29 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -2663,10 +2663,16 @@ try_combine (rtx i3, rtx i2, rtx i1, int *new_direct_jump_p)
 	  i2dest = SET_DEST (temp);
 	  i2dest_killed = dead_or_set_p (i2, i2dest);
 
+	  /* Replace the source in I2 with the new constant and make the
+	     resulting insn the new pattern for I3.  Then skip to where we
+	     validate the pattern.  Everything was set up above.  */
 	  SUBST (SET_SRC (temp),
 		 immed_double_const (olo, ohi, GET_MODE (SET_DEST (temp))));
 
 	  newpat = PATTERN (i2);
+
+          /* The dest of I3 has been replaced with the dest of I2.  */
+          changed_i3_dest = 1;
 	  goto validate_replacement;
 	}
     }
@@ -3038,8 +3044,6 @@ try_combine (rtx i3, rtx i2, rtx i1, int *new_direct_jump_p)
 	}
     }
 
-  /* We come here when we are replacing a destination in I2 with the
-     destination of I3.  */
  validate_replacement:
 
   /* Note which hard regs this insn has as inputs.  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 990ea36bf098..89469ada88f7 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2010-01-15  Jing Yu  <jingyu@google.com>
+
+	PR rtl-optimization/42691
+	* gcc.c-torture/execute/pr42691.c: New.
+
 2010-01-15  Richard Guenther  <rguenther@suse.de>
 
 	PR middle-end/42739
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr42691.c b/gcc/testsuite/gcc.c-torture/execute/pr42691.c
new file mode 100644
index 000000000000..321ac1befee1
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr42691.c
@@ -0,0 +1,40 @@
+extern void abort (void);
+
+union _D_rep
+{
+  unsigned short rep[4];
+  double val;
+};
+
+int add(double* key, double* table)
+{
+  unsigned i = 0;
+  double* deletedEntry = 0;
+  while (1) {
+    double* entry = table + i;
+
+    if (*entry == *key)
+      break;
+
+    union _D_rep _D_inf = {{ 0, 0, 0, 0x7ff0 }};
+    if (*entry != _D_inf.val)
+      abort ();
+
+    union _D_rep _D_inf2 = {{ 0, 0, 0, 0x7ff0 }};
+    if (!_D_inf2.val)
+      deletedEntry = entry;
+
+    i++;
+  }
+  *deletedEntry = 0.0;
+  return 0;
+}
+
+int main ()
+{
+  union _D_rep infinit = {{ 0, 0, 0, 0x7ff0 }};
+  double table[2] = { infinit.val, 23 };
+  double key = 23;
+  int ret = add (&key, table);
+  return ret;
+}