CSE optimization opportunities missed (68k)

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1 total messages Started by andrew morton Wed, 18 Nov 1992 17:03

#1419

Author: andrew morton
Date: Wed, 18 Nov 1992 17:03

46 lines
1263 bytes

A few things I have noticed in gcc2.2.2 (m68k):

The code

foo()
{
	bar(0x12345);
	bar(0x12345);
	bar(0x12345);
	bar(0x12345);
	bar(0x12345);
}

Doesn't put the constant into a register: it seems that
constant function arguments are being missed as CSE
candidates.

Also, in the code

foo(int a, int b, int c, int d)
{
	a += 0x12345;
	b += 0x12345;
	c += 0x12345;
	d += 0x12345;
	bar(a, b, c, d);
	zot(0x12345);
}

The constants used in the additions are held in a register
but that register is not used for the call to zot(): a constant
is pushed instead.

Thirdly, there seems to be a problem with -funroll-all-loops
and -frerun-cse-after-loops.  In the code

foo()
{
	int i;

	for (i = 0; i < 10; i++)
		bar();
}

The address of bar() is not held in a register after
unrolling.

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