🚀 go-pugleaf

But there is still a bug when using -fvolatile.

I tried following Mr. Kenner's advice and the load did not get compiled
away.  However, if I take the unannotated code and compile it with
-fvolatile, the fetch gets compiled away.  My understanding is that no
fetch should be compiled away if I do -fvolatile.

Contents:
 - a fragment of the mail message from Richard Kenner.
 - a new foo2.c file (with two tests, one using Kenner's advice and one
   with no (volatile) attribution.
 - a new foo2.s file, compiled with -fvolatile, that demonstrates that
   -fvolatile does not cause the fetch to be kept.
 - the wallpaper for how I compiled this.

Note:  This is on a sun4.
-Bradley
---- previous mail ----
   Date: Tue, 3 Nov 92 11:46:57 -0500
   From: kenner@vlsi1.ultra.nyu.edu (Richard Kenner)

	   ...(and even if I compile it with -fvolatile).

	   void test(void) {
	     (volatile)*((unsigned*)0x20000a20);
	   }

   Expressions aren't volatile, memory references are.  Try casting
   to (unsigned volatile *) instead of (unsigned *).

---- foo2.c ----
void test1(void) {
  *((unsigned volatile*)0x20000a20);
}

void test2(void) {
  *((unsigned*)0x20000a20);
}
---- foo2.s ----
gcc2_compiled.:
.stabs "/users/asd1/bradley/",100,0,0,Ltext0
.stabs "foo2.c",100,0,0,Ltext0
.text
Ltext0:
.stabs "int:t1=r1;-2147483648;2147483647;",128,0,0,0
.stabs "char:t2=r2;0;127;",128,0,0,0
.stabs "long int:t3=r1;-2147483648;2147483647;",128,0,0,0
.stabs "unsigned int:t4=r1;0;-1;",128,0,0,0
.stabs "long unsigned int:t5=r1;0;-1;",128,0,0,0
.stabs "short int:t6=r1;-32768;32767;",128,0,0,0
.stabs "long long int:t7=r1;0;-1;",128,0,0,0
.stabs "short unsigned int:t8=r1;0;65535;",128,0,0,0
.stabs "long long unsigned int:t9=r1;0;-1;",128,0,0,0
.stabs "signed char:t10=r1;-128;127;",128,0,0,0
.stabs "unsigned char:t11=r1;0;255;",128,0,0,0
.stabs "float:t12=r1;4;0;",128,0,0,0
.stabs "double:t13=r1;8;0;",128,0,0,0
.stabs "long double:t14=r1;8;0;",128,0,0,0
.stabs "void:t15=15",128,0,0,0
	.align 4
	.global _test1
	.proc	020
_test1:
.stabn 68,0,1,LM1
LM1:
	!#PROLOGUE# 0
	save %sp,-112,%sp
	!#PROLOGUE# 1
.stabn 68,0,2,LM2
LM2:
	sethi %hi(536873504),%g2
	ld [%g2+%lo(536873504)],%g2
.stabn 68,0,3,LM3
LM3:
	ret
	restore
.stabs "test1:F15",36,0,0,_test1
	.align 4
	.global _test2
	.proc	020
_test2:
.stabn 68,0,5,LM4
LM4:
	!#PROLOGUE# 0
	save %sp,-112,%sp
	!#PROLOGUE# 1
.stabn 68,0,7,LM5
LM5:
	ret
	restore
.stabs "test2:F15",36,0,0,_test2
---- the wallpaper ----
bradley@marley% gcc foo2.c -S -O -o foo2.s -Wall -g -v -fvolatile
Reading specs from /usr/local/lib/gcc-lib/sun4/2.2.2/specs
gcc version 2.2.2
 /usr/local/lib/gcc-lib/sun4/2.2.2/cpp -lang-c -v -undef -D__GNUC__=2 -Dsparc -Dsun -Dunix -D__sparc__ -D__sun__ -D__unix__ -D__sparc -D__sun -D__unix -D__OPTIMIZE__ -g -Wall foo2.c /usr/tmp/cca27379.i
GNU CPP version 2.2.2 (sparc)
 /usr/local/lib/gcc-lib/sun4/2.2.2/cc1 /usr/tmp/cca27379.i -quiet -dumpbase foo2.c -g -O -Wall -version -fvolatile -o foo2.s
GNU C version 2.2.2 (sparc) compiled by GNU C version 2.2.2.
foo2.c: In function `test2':
foo2.c:6: warning: statement with no effect
bradley@marley% 
---- that's all folks ----