[llvm-commits] [llvm] r47244 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/addnegneg.ll

[Chris Lattner]

Author: lattner
Date: Sun Feb 17 15:03:36 2008
New Revision: 47244

URL: http://llvm.org/viewvc/llvm-project?rev=47244&view=rev
Log:
Fold (-x + -y) -> -(x+y) which promotes better association, fixing
the second half of PR2047

Added:
    llvm/trunk/test/Transforms/InstCombine/addnegneg.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=47244&r1=47243&r2=47244&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sun Feb 17 15:03:36 2008
@@ -2090,8 +2090,16 @@
   }
 
   // -A + B  -->  B - A
-  if (Value *V = dyn_castNegVal(LHS))
-    return BinaryOperator::createSub(RHS, V);
+  // -A + -B  -->  -(A + B)
+  if (Value *LHSV = dyn_castNegVal(LHS)) {
+    if (Value *RHSV = dyn_castNegVal(RHS)) {
+      Instruction *NewAdd = BinaryOperator::createAdd(LHSV, RHSV, "sum");
+      InsertNewInstBefore(NewAdd, I);
+      return BinaryOperator::createNeg(NewAdd);
+    }
+    
+    return BinaryOperator::createSub(RHS, LHSV);
+  }
 
   // A + -B  -->  A - B
   if (!isa<Constant>(RHS))

Added: llvm/trunk/test/Transforms/InstCombine/addnegneg.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/addnegneg.ll?rev=47244&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/addnegneg.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/addnegneg.ll Sun Feb 17 15:03:36 2008
@@ -0,0 +1,12 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep { sub } | count 1
+; PR2047
+
+define i32 @l(i32 %a, i32 %b, i32 %c, i32 %d) {
+entry:
+	%b.neg = sub i32 0, %b		; <i32> [#uses=1]
+	%c.neg = sub i32 0, %c		; <i32> [#uses=1]
+	%sub4 = add i32 %c.neg, %b.neg		; <i32> [#uses=1]
+	%sub6 = add i32 %sub4, %d		; <i32> [#uses=1]
+	ret i32 %sub6
+}
+