From f1252a541ac87e814018c0dd01c39ea6356530eb Mon Sep 17 00:00:00 2001 From: Luc Van Oostenryck Date: Tue, 7 Feb 2017 21:50:26 +0100 Subject: [PATCH] simplify '(x * -1)' to '-x' Currently we simplify multiplication by 1 but nothing is done for multiplication by -1 which is equivalent to the negation of its first operand. This patch add this simplification. Also add small test cases showing the simplification. Signed-off-by: Luc Van Oostenryck Signed-off-by: Christopher Li --- simplify.c | 11 +++++++++++ validation/optim/muldiv-minus-one.c | 13 +++++++++++++ 2 files changed, 24 insertions(+) create mode 100644 validation/optim/muldiv-minus-one.c diff --git a/simplify.c b/simplify.c index ed6cc41b..e529cee3 100644 --- a/simplify.c +++ b/simplify.c @@ -339,6 +339,9 @@ static int simplify_asr(struct instruction *insn, pseudo_t pseudo, long long val static int simplify_mul_div(struct instruction *insn, long long value) { + unsigned long long sbit = 1ULL << (insn->size - 1); + unsigned long long bits = sbit | (sbit - 1); + if (value == 1) return replace_with_pseudo(insn, insn->src1); @@ -347,6 +350,14 @@ static int simplify_mul_div(struct instruction *insn, long long value) case OP_MULU: if (value == 0) return replace_with_pseudo(insn, insn->src2); + if (!(value & sbit)) // positive + break; + + value |= ~bits; + if (value == -1) { + insn->opcode = OP_NEG; + return REPEAT_CSE; + } } return 0; diff --git a/validation/optim/muldiv-minus-one.c b/validation/optim/muldiv-minus-one.c new file mode 100644 index 00000000..729b7344 --- /dev/null +++ b/validation/optim/muldiv-minus-one.c @@ -0,0 +1,13 @@ +typedef unsigned int u32; + +int smulm1(int a) { return a * -1; } +u32 umulm1(u32 a) { return a * (u32) -1; } + +/* + * check-name: muldiv-minus-one + * check-command: test-linearize -Wno-decl $file + * check-output-ignore + * + * check-output-excludes: mul[us]\\. + * check-output-contains: neg\\. + */ -- 2.11.4.GIT