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+#if 0
+/*
+Date: Mon, 17 Aug 87 09:03:50 PDT
+From: bruce@stride.stride.com (Bruce Robertson)
+To: bug-gcc@prep.ai.mit.edu
+Subject: Optimizer bug in gcc 1.x
+
+I found the cause of the optimizer bug that I've been sending you.  It
+occurs because you scan for the first and last occurances of registers
+before common subexpression processing, but cse can change these
+occurances.  The bug appears in the example program because loop
+optimization removes a load of "mem" into a pseudo-register, because
+based on the information of the register scan it thinks that there are
+no more appearances of the pseudo-register.  Cse added a reference,
+however, and this information is not placed in regno_last_uid[].  The
+solution seems to be to call reg_scan() again after calling
+cse_main().  It fixed the bug anyway, and didn't seem to cause
+anything bad.
+
+Diffs for the fix, and the original sample program follow.
+
+
+Diffs:
+======================================================================
+*** /tmp/,RCSt1a00495	Thu Aug 13 13:09:01 1987
+--- toplev.c	Thu Aug 13 13:08:39 1987
+***************
+*** 776,781 ****
+--- 776,786 ----
+  
+        TIMEVAR (cse_time, tem = cse_main (insns, max_reg_num ()));
+  
++       /* We need to scan for registers again, because common subexpression
++ 	 elimination could have rearranged the first and last occurrances
++ 	 of registers. */
++       TIMEVAR (cse_time, reg_scan (insns, max_reg_num ()));
++ 
+        if (tem)
+  	TIMEVAR (jump_time, jump_optimize (insns, 0, 0));
+      }
+
+
+
+Sample program:
+======================================================================
+#endif
+
+typedef unsigned char quarterword;
+typedef unsigned short halfword;
+
+typedef union
+{ 
+    struct { 
+        halfword    lh; 
+        halfword    rh; 
+    } hh1; 
+    struct { 
+        quarterword b0; 
+        quarterword b1; 
+        halfword    rh; 
+    } hh2; 
+}
+    two_halves;
+
+typedef struct
+{ 
+    quarterword b0;
+    quarterword b1;
+    quarterword b2;
+    quarterword b3;
+}
+    four_quarters;
+
+typedef union
+{ 
+    int         i;   
+    float      gr;  
+    two_halves      hh;  
+    four_quarters   qqqq;
+}
+    memory_word;
+
+memory_word     mem[10];
+
+unsigned int fewest_demerits;
+unsigned short best_bet = 0;
+unsigned short best_line = -1;
+
+
+void
+foo(r)
+	unsigned short r;
+{
+
+	do {
+		if (mem[r].hh.hh2.b0 != 2 &&
+		    mem[(r) + 2].i < fewest_demerits) {
+                        best_bet = r;
+		}
+		r = mem[r].hh.hh1.rh;
+	} while (r != (65501 - 7));
+
+	/*
+	 * This is the statement that is causing trouble.  See the comment
+	 * in the assembly code below.
+	 */
+	best_line = mem[best_bet + 1].hh.hh1.lh;
+}
+
+main()
+{
+	mem[0].hh.hh2.b0 = 0;
+	mem[0].hh.hh1.rh = 65501-7;
+	mem[1].hh.hh1.lh = 456;
+	mem[2].i = 30;
+	foo(0);
+	if (best_line == 456)
+		printf("Test passed\n");
+	else
+		printf("Test failed, best_line = %d\n", best_line);
+}
+
+/*
+
+#NO_APP
+.comm _fewest_demerits,4
+.comm _best_bet,2
+.comm _best_line,2
+.globl _foo
+.text
+	.even
+_foo:
+	link a6,#0
+	moveml #0x3000,sp@-
+	movew #1,d0
+	clrl d1
+	clrl d2
+	lea _mem,a0
+L2:
+	movew d0,d1
+	cmpb #2,a0@(d1:l:4)
+	jeq L4
+	movel a0@(8,d1:l:4),d3
+	cmpl _fewest_demerits,d3
+	jcc L4
+	movew d0,_best_bet
+L4:
+	movew d0,d2
+	movew a0@(2,d2:l:4),d0
+	cmpw #65494,d0
+	jne L2
+	clrl d0
+	movew _best_bet,d0
+
+|
+|	Where did this reference (below) to A1 come from?  It should be A0,
+|	since that still points to "mem".  A1 is never set in the code
+|	above.
+|
+|	When this code fragment is in place in Common Tex (in function
+|	"line_break()" in file "par.c") the reference is to -4(fp)
+|	rather than A1.
+|
+
+	movew a1@(4,d0:l:4),_best_line
+	moveml a6@(-8),#0xc
+	unlk a6
+	rts
+*/