[llvm] r243500 - ignore duplicate divisor uses when transforming into reciprocal multiplies (PR24141)

[Sanjay Patel]

Author: spatel
Date: Tue Jul 28 18:28:22 2015
New Revision: 243500

URL: http://llvm.org/viewvc/llvm-project?rev=243500&view=rev
Log:
ignore duplicate divisor uses when transforming into reciprocal multiplies (PR24141)

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


Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
    llvm/trunk/test/CodeGen/X86/fdiv-combine.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=243500&r1=243499&r2=243500&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Tue Jul 28 18:28:22 2015
@@ -8261,11 +8261,11 @@ SDValue DAGCombiner::combineRepeatedFPDi
     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.

Modified: llvm/trunk/test/CodeGen/X86/fdiv-combine.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/fdiv-combine.ll?rev=243500&r1=243499&r2=243500&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/fdiv-combine.ll (original)
+++ llvm/trunk/test/CodeGen/X86/fdiv-combine.ll Tue Jul 28 18:28:22 2015
@@ -44,5 +44,24 @@ define double @div3_arcp(double %x, doub
   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" }