scc

Simple C99 Compiler
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commit c9538a1cb5279a7a70695c86ad31ea9f85436d59
parent 19e83e69aa412cea8f41a28506cc9bfcc84525c4
Author: Roberto E. Vargas Caballero <k0ga@shike2.com>
Date:   Wed,  2 Sep 2015 14:57:54 +0200

Add more algebraic identities

Diffstat:
cc1/fold.c | 77+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----------------
1 file changed, 61 insertions(+), 16 deletions(-)

diff --git a/cc1/fold.c b/cc1/fold.c @@ -376,36 +376,81 @@ ones(int n) return v; } +/* + * i || 0 => i,0 + * i || 1 => i + * i && 0 => i,0 + * i && 1 => i + * i >> 0 => i + * i << 0 => i + * i + 0 => i + * i - 0 => i + * i | 0 => i + * i ^ 0 => i + * i * 0 => i,0 + * i * 1 => i + * i / 1 => i + * i & ~0 => i + * i % 1 => i,1 + */ static Node * -identity(int op, Node *lp, Node *rp) +identity(int *op, Node *lp, Node *rp) { - int val; + int iszero, isone, istrue; - switch (op) { + if (!rp) + return NULL; + + iszero = cmpnode(rp, 0); + isone = cmpnode(rp, 1), + istrue = !iszero && rp->constant; + + switch (*op) { + case OOR: + if (istrue) + goto change_to_comma; + if (iszero) + break; + return NULL; + case OAND: + if (iszero) + goto change_to_comma; + if (istrue) + break; + return NULL; case OSHL: case OSHR: case OBXOR: case OADD: + case OBOR: case OSUB: - val = 0; - break; - case ODIV: - case OMOD: + if (iszero) + break; + return NULL; case OMUL: - case OBOR: - val = 1; - break; + if (iszero) + goto change_to_comma; + case ODIV: + if (isone) + break; + return NULL; case OBAND: - if (cmpnode(lp, ones(lp->type->size * 8))) - goto free_right; + if (cmpnode(rp, ones(lp->type->size * 8))) + break; + return NULL; + case OMOD: + if (isone) + goto change_to_comma; default: return NULL; } - if (!cmpnode(rp, val)) - return NULL; -free_right: + freetree(rp); return lp; + +change_to_comma: + *op = OCOMMA; + return NULL; } Node * @@ -416,7 +461,7 @@ simplify(int op, Type *tp, Node *lp, Node *rp) commutative(&op, &lp, &rp); if ((np = fold(op, tp, lp, rp)) != NULL) return np; - if ((np = identity(op, lp, rp)) != NULL) + if ((np = identity(&op, lp, rp)) != NULL) return np; return node(op, tp, lp, rp); }