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ignore duplicate divisor uses when transforming into reciprocal multiplies (PR24141)

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PR24141: https://llvm.org/bugs/show_bug.cgi?id=24141
contains a test case where we have duplicate entries in a node's uses() list.

After r241826, we use CombineTo() to delete dead nodes when combining the uses into
reciprocal multiplies, but this fails if we encounter the just-deleted node again in
the list.

The solution in this patch is to not add duplicate entries to the list of users that
we will subsequently iterate over. For the test case, this avoids triggering the
combine divisors logic entirely because there really is only one user of the divisor.

Differential Revision: http://reviews.llvm.org/D11345



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243500 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjay Patel 2015-07-28 23:28:22 +00:00
parent 6ea347b66f
commit 8fd3ed9e3a
2 changed files with 23 additions and 4 deletions
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8
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -8261,11 +8261,11 @@ SDValue DAGCombiner::combineRepeatedFPDivisors(SDNode *N) {
return SDValue();
// Find all FDIV users of the same divisor.
SmallVector<SDNode *, 4> Users;
for (auto *U : N1->uses()) {
// Use a set because duplicates may be present in the user list.
SetVector<SDNode *> Users;
for (auto *U : N1->uses())
if (U->getOpcode() == ISD::FDIV && U->getOperand(1) == N1)
Users.push_back(U);
}
Users.insert(U);
// Now that we have the actual number of divisor uses, make sure it meets
// the minimum threshold specified by the target.

19
test/CodeGen/X86/fdiv-combine.ll
View File

@ -44,5 +44,24 @@ define double @div3_arcp(double %x, double %y, double %z) #0 {
ret double %ret
}
define void @PR24141() #0 {
; CHECK-LABEL: PR24141:
; CHECK: callq
; CHECK-NEXT: divsd
; CHECK-NEXT: jmp
entry:
br label %while.body
while.body:
%x.0 = phi double [ undef, %entry ], [ %div, %while.body ]
%call = call { double, double } @g(double %x.0)
%xv0 = extractvalue { double, double } %call, 0
%xv1 = extractvalue { double, double } %call, 1
%div = fdiv double %xv0, %xv1
br label %while.body
}
declare { double, double } @g(double)
; FIXME: If the backend understands 'arcp', then this attribute is unnecessary.
attributes #0 = { "unsafe-fp-math"="true" }