/// NOTE: This routine will set operands of non-leaf non-root nodes to undef in
/// order to ensure that every non-root node in the expression has *exactly one*
/// use by a non-leaf node of the expression. This destruction means that the
-/// caller MUST use something like RewriteExprTree to put the values back in.
+/// caller MUST either replace 'I' with a new expression or use something like
+/// RewriteExprTree to put the values back in.
///
/// In the above example either the right operand of A or the left operand of B
/// will be replaced by undef. If it is B's operand then this gives:
/// / \ / \ / \ |
/// + * | F, G
///
-/// Note that if you visit operands recursively starting from a leaf node then
-/// you will never encounter such an undef operand unless you get back to 'I',
+/// Note that such undef operands can only be reached by passing through 'I'.
+/// For example, if you visit operands recursively starting from a leaf node
+/// then you will never see such an undef operand unless you get back to 'I',
/// which requires passing through a phi node.
///
/// Note that this routine may also mutate binary operators of the wrong type
unsigned Opcode = I->getOpcode();
NodesToRewrite.push_back(I);
- // ExpressionChanged - Whether the rewritten expression differs non-trivially
- // from the original, requiring the clearing of all optional flags.
- bool ExpressionChanged = false;
+ // ExpressionChanged - Non-null if the rewritten expression differs from the
+ // original in some non-trivial way, requiring the clearing of optional flags.
+ // Flags are cleared from the operator in ExpressionChanged up to I inclusive.
+ BinaryOperator *ExpressionChanged = 0;
BinaryOperator *Previous;
BinaryOperator *Op = 0;
for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
assert(!NodesToRewrite.empty() &&
"Optimized expressions has more nodes than original!");
Previous = Op; Op = NodesToRewrite.pop_back_val();
- // Compactify the tree instructions together with each other to guarantee
- // that the expression tree is dominated by all of Ops.
- if (Previous)
+ if (ExpressionChanged)
+ // Compactify the tree instructions together with each other to guarantee
+ // that the expression tree is dominated by all of Ops.
Op->moveBefore(Previous);
// The last operation (which comes earliest in the IR) is special as both
}
DEBUG(dbgs() << "TO: " << *Op << '\n');
- ExpressionChanged = true;
+ ExpressionChanged = Op;
MadeChange = true;
++NumChanged;
if (BinaryOperator *BO = isReassociableOp(Op->getOperand(1), Opcode))
NodesToRewrite.push_back(BO);
Op->setOperand(1, NewRHS);
- ExpressionChanged = true;
+ ExpressionChanged = Op;
}
DEBUG(dbgs() << "TO: " << *Op << '\n');
MadeChange = true;
DEBUG(dbgs() << "RA: " << *Op << '\n');
Op->setOperand(0, NodesToRewrite.back());
DEBUG(dbgs() << "TO: " << *Op << '\n');
- ExpressionChanged = true;
+ ExpressionChanged = Op;
MadeChange = true;
++NumChanged;
}
- // If the expression changed non-trivially then clear out all subclass data in
- // the entire rewritten expression.
+ // If the expression changed non-trivially then clear out all subclass data
+ // starting from the operator specified in ExpressionChanged.
if (ExpressionChanged) {
do {
- Op->clearSubclassOptionalData();
- if (Op == I)
+ ExpressionChanged->clearSubclassOptionalData();
+ if (ExpressionChanged == I)
break;
- Op = cast<BinaryOperator>(*Op->use_begin());
+ ExpressionChanged = cast<BinaryOperator>(*ExpressionChanged->use_begin());
} while (1);
}
--- /dev/null
+; RUN: opt < %s -reassociate -S | FileCheck %s
+
+; When there is nothing to do, or not much to do, check that reassociate leaves
+; things alone.
+
+declare void @use(i32)
+
+define void @test1(i32 %a, i32 %b) {
+; Shouldn't change or move any of the add instructions. Should commute but
+; otherwise not change or move any of the mul instructions.
+; CHECK: @test1
+ %a0 = add nsw i32 %a, 1
+; CHECK-NEXT: %a0 = add nsw i32 %a, 1
+ %m0 = mul nsw i32 3, %a
+; CHECK-NEXT: %m0 = mul nsw i32 %a, 3
+ %a1 = add nsw i32 %a0, %b
+; CHECK-NEXT: %a1 = add nsw i32 %a0, %b
+ %m1 = mul nsw i32 %b, %m0
+; CHECK-NEXT: %m1 = mul nsw i32 %m0, %b
+ call void @use(i32 %a1)
+; CHECK-NEXT: call void @use
+ call void @use(i32 %m1)
+ ret void
+}
+
+define void @test2(i32 %a, i32 %b, i32 %c, i32 %d) {
+; The initial add doesn't change so should not lose the nsw flag.
+; CHECK: @test2
+ %a0 = add nsw i32 %b, %a
+; CHECK-NEXT: %a0 = add nsw i32 %b, %a
+ %a1 = add nsw i32 %a0, %d
+; CHECK-NEXT: %a1 = add i32 %a0, %c
+ %a2 = add nsw i32 %a1, %c
+; CHECK-NEXT: %a2 = add i32 %a1, %d
+ call void @use(i32 %a2)
+; CHECK-NEXT: call void @use
+ ret void
+}