[PATCH] D11345: ignore duplicate divisor uses when transforming into reciprocal multiplies (PR24141)

[Sanjay Patel]

spatel updated this revision to Diff 30192.
spatel added a comment.

Patch updated:
I just discovered 'SmallPtrSet'. 
Looks like it was designed exactly for this case, so let's use it here instead of a vector. Then, we don't have to use std::find() for dup checking.


http://reviews.llvm.org/D11345

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/X86/fdiv-combine.ll

Index: test/CodeGen/X86/fdiv-combine.ll
===================================================================
--- test/CodeGen/X86/fdiv-combine.ll
+++ test/CodeGen/X86/fdiv-combine.ll
@@ -44,5 +44,24 @@
   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" }
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8366,12 +8366,12 @@
     if (N0CFP && N0CFP->isExactlyValue(1.0))
       return SDValue();
 
-    SmallVector<SDNode *, 4> Users;
+    // Only count unique users; duplicates may be present in the user list.
+    SmallPtrSet<SDNode*, 4> Users;
     // Find all FDIV users of the same divisor.
-    for (auto *U : N1->uses()) {
+    for (auto *U : N1->uses())
       if (U->getOpcode() == ISD::FDIV && U->getOperand(1) == N1)
-        Users.push_back(U);
-    }
+        Users.insert(U);
 
     if (TLI.combineRepeatedFPDivisors(Users.size())) {
       SDValue FPOne = DAG.getConstantFP(1.0, DL, VT);


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