From 133e68b45cea9fa52c9a519bf287c6eea8ed5bba Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Tue, 28 Jul 2015 23:28:22 +0000
Subject: [PATCH] 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

llvm-svn: 243500
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp |  8 ++++----
 llvm/test/CodeGen/X86/fdiv-combine.ll         | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index de26516..3fe6636 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -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.
diff --git a/llvm/test/CodeGen/X86/fdiv-combine.ll b/llvm/test/CodeGen/X86/fdiv-combine.ll
index 34eac62..b65e9d0 100644
--- a/llvm/test/CodeGen/X86/fdiv-combine.ll
+++ b/llvm/test/CodeGen/X86/fdiv-combine.ll
@@ -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" }
-- 
2.7.4