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(fold_rtx): Alter previous change: don't fold the shift 

if the count exceeds the width of the value inside the subreg.

(note_mem_written): (mem (scratch)) means clobber everything.

(fold_rtx): Special case handling for folding
a subreg of the result of a left shift.

From-SVN: r5854
This commit is contained in:
Richard Stallman 1993-10-21 02:43:58 +00:00
parent cc8187fc1d
commit 76fb0b6041
1 changed files with 26 additions and 1 deletions
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27
gcc/cse.c
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@ -4729,7 +4729,29 @@ fold_rtx (x, insn)
if (op1)
op1 = equiv_constant (op1);
if (op0 && op1)
/* If we are looking for the low SImode part of
(ashift:DI c (const_int 32)), it doesn't work
to compute that in SImode, because a 32-bit shift
in SImode is unpredictable. We know the value is 0. */
if (op0 && op1
&& (GET_CODE (elt->exp) == ASHIFT
|| GET_CODE (elt->exp) == LSHIFT)
&& GET_CODE (op1) == CONST_INT
&& INTVAL (op1) >= GET_MODE_BITSIZE (mode))
{
if (INTVAL (op1) < GET_MODE_BITSIZE (GET_MODE (elt->exp)))
/* If the count fits in the inner mode's width,
but exceeds the outer mode's width,
the value will get truncated to 0
by the subreg. */
new = const0_rtx;
else
/* If the count exceeds even the inner mode's width,
don't fold this expression. */
new = 0;
}
else if (op0 && op1)
new = simplify_binary_operation (GET_CODE (elt->exp), mode,
op0, op1);
}
@ -7101,6 +7123,9 @@ note_mem_written (written, writes_ptr)
}
else if (GET_MODE (written) == BLKmode)
*writes_ptr = everything;
/* (mem (scratch)) means clobber everything. */
else if (GET_CODE (addr) == SCRATCH)
*writes_ptr = everything;
else if (cse_rtx_addr_varies_p (written))
{
/* A varying address that is a sum indicates an array element,