One more permutation of subtracting off a base value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61361 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 783bfce9cc39d211dff083bb9c65f7796f7da973..e3525df181ab2bbca3c0ba2ed69b1d521fb7381d 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1184,6 +1184,12 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
       N0.getOperand(1).getOperand(0) == N1)
     return DAG.getNode(ISD::SUB, VT, N0.getOperand(0), 
                                      N0.getOperand(1).getOperand(1));
+  // fold ((A-(B-C))-C) -> A-B
+  if (N0.getOpcode() == ISD::SUB &&
+      N0.getOperand(1).getOpcode() == ISD::SUB &&
+      N0.getOperand(1).getOperand(1) == N1)
+    return DAG.getNode(ISD::SUB, VT, N0.getOperand(0), 
+                                     N0.getOperand(1).getOperand(0));
   // fold (sub x, (select cc, 0, c)) -> (select cc, x, (sub, x, c))
   if (N1.getOpcode() == ISD::SELECT && N1.getNode()->hasOneUse()) {
     SDValue Result = combineSelectAndUse(N, N1, N0, DAG, TLI, LegalOperations);

diff --git a/test/CodeGen/X86/2008-12-22-dagcombine-5.ll b/test/CodeGen/X86/2008-12-22-dagcombine-5.ll
new file mode 100644 (file)
index 0000000..24be521
--- /dev/null
+++ b/test/CodeGen/X86/2008-12-22-dagcombine-5.ll
@@ -0,0 +1,14 @@
+; RUN: llvm-as < %s | llc -march=x86 | grep "(%esp)" | count 2
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target triple = "i386-apple-darwin9.5"
+; -(-a) - a should be found and removed, leaving refs to only L and P
+define i32 @test(i32 %a, i32 %L, i32 %P) nounwind {
+entry:
+        %0 = sub i32 %L, %a
+        %1 = sub i32 %P, %0
+       %2 = sub i32 %1, %a
+       br label %return
+
+return:                ; preds = %bb3
+       ret i32 %2
+}