The following patch is an attempt to finally fully close PR middle-end/21137. As explained in the PR, my original patch from 2006 didn't handle the case where there's a sign preserving NOP in the tree. Easily fixed by calling tree_strip_nop_conversions at the appropriate point in fold-const.c. Most of this patch is the resulting re-indentation.
Test on x86_64-pc-linux-gnu with "make bootstrap" and "make check" with no
regressions.
Ok for mainline?
2016-08-05 Roger Sayle <ro...@nextmovesoftware.com>
PR middle-end/21137
* fold-const.c (fold_binary_loc) <EQ_EXPR>: Allow transformations of
((T)(X>>C1)&C2) eq/ne 0 when the cast (T) is a sign preserving NOP by
calling tree_strip_nop_conversions.
* gcc.dg/fold-eqandshift-4.c: New test case.
Roger
--
Roger Sayle, Ph.D.
CEO and founder
NextMove Software Limited
Registered in England No. 07588305
Registered Office: Innovation Centre (Unit 23), Cambridge Science Park,
Cambridge CB4 0EY
Index: fold-const.c
===================================================================
*** fold-const.c (revision 238992)
--- fold-const.c (working copy)
*************** fold_binary_loc (location_t loc,
*** 10604,10648 ****
C1 is a valid shift constant, and C2 is a power of two, i.e.
a single bit. */
if (TREE_CODE (arg0) == BIT_AND_EXPR
- && TREE_CODE (TREE_OPERAND (arg0, 0)) == RSHIFT_EXPR
- && TREE_CODE (TREE_OPERAND (TREE_OPERAND (arg0, 0), 1))
- == INTEGER_CST
&& integer_pow2p (TREE_OPERAND (arg0, 1))
&& integer_zerop (arg1))
{
! tree itype = TREE_TYPE (arg0);
! tree arg001 = TREE_OPERAND (TREE_OPERAND (arg0, 0), 1);
! prec = TYPE_PRECISION (itype);
! /* Check for a valid shift count. */
! if (wi::ltu_p (arg001, prec))
! {
! tree arg01 = TREE_OPERAND (arg0, 1);
! tree arg000 = TREE_OPERAND (TREE_OPERAND (arg0, 0), 0);
! unsigned HOST_WIDE_INT log2 = tree_log2 (arg01);
! /* If (C2 << C1) doesn't overflow, then ((X >> C1) & C2) != 0
! can be rewritten as (X & (C2 << C1)) != 0. */
! if ((log2 + TREE_INT_CST_LOW (arg001)) < prec)
{
! tem = fold_build2_loc (loc, LSHIFT_EXPR, itype, arg01,
arg001);
! tem = fold_build2_loc (loc, BIT_AND_EXPR, itype, arg000, tem);
! return fold_build2_loc (loc, code, type, tem,
! fold_convert_loc (loc, itype, arg1));
! }
! /* Otherwise, for signed (arithmetic) shifts,
! ((X >> C1) & C2) != 0 is rewritten as X < 0, and
! ((X >> C1) & C2) == 0 is rewritten as X >= 0. */
! else if (!TYPE_UNSIGNED (itype))
! return fold_build2_loc (loc, code == EQ_EXPR ? GE_EXPR :
LT_EXPR, type,
! arg000, build_int_cst (itype, 0));
! /* Otherwise, of unsigned (logical) shifts,
! ((X >> C1) & C2) != 0 is rewritten as (X,false), and
! ((X >> C1) & C2) == 0 is rewritten as (X,true). */
! else
! return omit_one_operand_loc (loc, type,
code == EQ_EXPR ? integer_one_node
: integer_zero_node,
arg000);
}
}
--- 10604,10654 ----
C1 is a valid shift constant, and C2 is a power of two, i.e.
a single bit. */
if (TREE_CODE (arg0) == BIT_AND_EXPR
&& integer_pow2p (TREE_OPERAND (arg0, 1))
&& integer_zerop (arg1))
{
! tree arg00 = tree_strip_nop_conversions (TREE_OPERAND (arg0, 0));
! if (TREE_CODE (arg00) == RSHIFT_EXPR
! && TREE_CODE (TREE_OPERAND (arg00, 1)) == INTEGER_CST)
! {
! tree itype = TREE_TYPE (arg0);
! tree arg001 = TREE_OPERAND (arg00, 1);
! prec = TYPE_PRECISION (itype);
! /* Check for a valid shift count. */
! if (wi::ltu_p (arg001, prec))
{
! tree arg01 = TREE_OPERAND (arg0, 1);
! tree arg000 = TREE_OPERAND (arg00, 0);
! unsigned HOST_WIDE_INT log2 = tree_log2 (arg01);
! /* If (C2 << C1) doesn't overflow, then ((X >> C1) & C2) != 0
! can be rewritten as (X & (C2 << C1)) != 0. */
! if ((log2 + TREE_INT_CST_LOW (arg001)) < prec)
! {
! tree tem2 = fold_convert_loc (loc, itype, arg1);
! tem = fold_build2_loc (loc, LSHIFT_EXPR, itype,
! arg01, arg001);
! tem = fold_build2_loc (loc, BIT_AND_EXPR, itype,
! arg000, tem);
! return fold_build2_loc (loc, code, type, tem, tem2);
! }
! /* Otherwise, for signed (arithmetic) shifts,
! ((X >> C1) & C2) != 0 is rewritten as X < 0, and
! ((X >> C1) & C2) == 0 is rewritten as X >= 0. */
! else if (!TYPE_UNSIGNED (itype))
! return fold_build2_loc (loc,
! code == EQ_EXPR ? GE_EXPR : LT_EXPR,
! type, arg000,
! build_int_cst (itype, 0));
! /* Otherwise, of unsigned (logical) shifts,
! ((X >> C1) & C2) != 0 is rewritten as (X,false), and
! ((X >> C1) & C2) == 0 is rewritten as (X,true). */
! else
! return omit_one_operand_loc (loc, type,
code == EQ_EXPR ? integer_one_node
: integer_zero_node,
arg000);
+ }
}
}
fold-eqandshift-4.c
Description: Binary data
