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| author | sayle <sayle@138bc75d-0d04-0410-961f-82ee72b054a4> | 2006-02-26 15:36:52 +0000 |
|---|---|---|
| committer | sayle <sayle@138bc75d-0d04-0410-961f-82ee72b054a4> | 2006-02-26 15:36:52 +0000 |
| commit | 1d8ff0d259a49c3a172fb5ef215cb01dcec2605e (patch) | |
| tree | 54fbe907a418470a9df428739064819f26fcfdfd /gcc/fold-const.c | |
| parent | 17e07532908dfd39ea8eb0815aaae951946505bf (diff) | |
| download | gcc-1d8ff0d259a49c3a172fb5ef215cb01dcec2605e.tar.gz | |
2006-02-26 Roger Sayle <roger@eyesopen.com>
James A. Morrison <phython@gcc.gnu.org>
PR middle-end/21137
* fold-const.c (fold_binary) <EQ_EXPR>: Fold ((X>>C1)&C2) eq/ne 0,
when C2 is a power of two, as either (X&(C2<<C1)) eq/ne 0 if the
new constant C2<<C1, or as (X<0) or (X,false) depending upon the
signedness of the shift operation.
* gcc.dg/fold-eqandshift-1.c: New test case.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@111453 138bc75d-0d04-0410-961f-82ee72b054a4
Diffstat (limited to 'gcc/fold-const.c')
| -rw-r--r-- | gcc/fold-const.c | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/gcc/fold-const.c b/gcc/fold-const.c index 3c3852bc158..7eb4d914e92 100644 --- a/gcc/fold-const.c +++ b/gcc/fold-const.c @@ -9653,6 +9653,52 @@ fold_binary (enum tree_code code, tree type, tree op0, tree op1) fold_convert (newtype, arg1)); } + /* Fold ((X >> C1) & C2) == 0 and ((X >> C1) & C2) != 0 where + 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); + unsigned HOST_WIDE_INT prec = TYPE_PRECISION (itype); + tree arg001 = TREE_OPERAND (TREE_OPERAND (arg0, 0), 1); + + /* Check for a valid shift count. */ + if (TREE_INT_CST_HIGH (arg001) == 0 + && TREE_INT_CST_LOW (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 (arg01)) < prec) + { + tem = fold_build2 (LSHIFT_EXPR, itype, arg01, arg001); + tem = fold_build2 (BIT_AND_EXPR, itype, arg000, tem); + return fold_build2 (code, type, tem, 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 (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 (type, + code == EQ_EXPR ? integer_one_node + : integer_zero_node, + arg000); + } + } + /* If this is an NE comparison of zero with an AND of one, remove the comparison since the AND will give the correct value. */ if (code == NE_EXPR |