Teach GVN that x+y is the same as y+x and that x<y is the same as y>x.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151365 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 39 insertions, 1 deletions

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 5b95f5b86f..162ee2b5ce 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -154,9 +154,24 @@ Expression ValueTable::create_expression(Instruction *I) {
   for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
        OI != OE; ++OI)
     e.varargs.push_back(lookup_or_add(*OI));
+  if (I->isCommutative()) {
+    // Ensure that commutative instructions that only differ by a permutation
+    // of their operands get the same value number by sorting the operand value
+    // numbers.  Since all commutative instructions have two operands it is more
+    // efficient to sort by hand rather than using, say, std::sort.
+    assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!");
+    if (e.varargs[0] > e.varargs[1])
+      std::swap(e.varargs[0], e.varargs[1]);
+  }
   
   if (CmpInst *C = dyn_cast<CmpInst>(I)) {
-    e.opcode = (C->getOpcode() << 8) | C->getPredicate();
+    // Sort the operand value numbers so x<y and y>x get the same value number.
+    CmpInst::Predicate Predicate = C->getPredicate();
+    if (e.varargs[0] > e.varargs[1]) {
+      std::swap(e.varargs[0], e.varargs[1]);
+      Predicate = CmpInst::getSwappedPredicate(Predicate);
+    }
+    e.opcode = (C->getOpcode() << 8) | Predicate;
   } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) {
     for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end();
          II != IE; ++II)
diff --git a/test/Transforms/GVN/commute.ll b/test/Transforms/GVN/commute.ll
new file mode 100644
index 0000000000..cf4fb7f172
--- /dev/null
+++ b/test/Transforms/GVN/commute.ll
@@ -0,0 +1,23 @@
+; RUN: opt -gvn -S < %s | FileCheck %s
+
+declare void @use(i32, i32)
+
+define void @foo(i32 %x, i32 %y) {
+  ; CHECK: @foo
+  %add1 = add i32 %x, %y
+  %add2 = add i32 %y, %x
+  call void @use(i32 %add1, i32 %add2)
+  ; CHECK: @use(i32 %add1, i32 %add1)
+  ret void
+}
+
+declare void @vse(i1, i1)
+
+define void @bar(i32 %x, i32 %y) {
+  ; CHECK: @bar
+  %cmp1 = icmp ult i32 %x, %y
+  %cmp2 = icmp ugt i32 %y, %x
+  call void @vse(i1 %cmp1, i1 %cmp2)
+  ; CHECK: @vse(i1 %cmp1, i1 %cmp1)
+  ret void
+}