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 <luc.vanoostenryck@xxxxxxxxx>
---
simplify.c | 12 ++++++++++++
validation/optim/muldiv-minus-one.c | 13 +++++++++++++
2 files changed, 25 insertions(+)
create mode 100644 validation/optim/muldiv-minus-one.c
diff --git a/simplify.c b/simplify.c
index 5541fc4c..6c7c79e9 100644
--- a/simplify.c
+++ b/simplify.c
@@ -312,6 +312,9 @@ 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);
@@ -320,6 +323,15 @@ 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;
+ }
/* Fall through */
case OP_DIVS:
case OP_DIVU:
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\\.
+ */
--
2.10.2
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