[llvm-commits] [llvm] r73664 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/xor-and.ll

[Dan Gohman]

Author: djg
Date: Wed Jun 17 19:00:20 2009
New Revision: 73664

URL: http://llvm.org/viewvc/llvm-project?rev=73664&view=rev
Log:
Teach ScalarEvolution how to recognize another xor(and(x, C), C) case.
If C is a single bit and the and gets analyzed as a truncate and
zero-extend, the xor can be represnted as an add.

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/test/Analysis/ScalarEvolution/xor-and.ll

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=73664&r1=73663&r2=73664&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed Jun 17 19:00:20 2009
@@ -2453,10 +2453,25 @@
               LCI->getValue() == CI->getValue())
             if (const SCEVZeroExtendExpr *Z =
                   dyn_cast<SCEVZeroExtendExpr>(getSCEV(U->getOperand(0)))) {
-              SCEVHandle ZO = Z->getOperand();
-              if (APIntOps::isMask(getTypeSizeInBits(ZO->getType()),
-                                   CI->getValue()))
-                return getZeroExtendExpr(getNotSCEV(ZO), U->getType());
+              const Type *UTy = U->getType();
+              SCEVHandle Z0 = Z->getOperand();
+              const Type *Z0Ty = Z0->getType();
+              unsigned Z0TySize = getTypeSizeInBits(Z0Ty);
+
+              // If C is a low-bits mask, the zero extend is zerving to
+              // mask off the high bits. Complement the operand and
+              // re-apply the zext.
+              if (APIntOps::isMask(Z0TySize, CI->getValue()))
+                return getZeroExtendExpr(getNotSCEV(Z0), UTy);
+
+              // If C is a single bit, it may be in the sign-bit position
+              // before the zero-extend. In this case, represent the xor
+              // using an add, which is equivalent, and re-apply the zext.
+              APInt Trunc = APInt(CI->getValue()).trunc(Z0TySize);
+              if (APInt(Trunc).zext(getTypeSizeInBits(UTy)) == CI->getValue() &&
+                  Trunc.isSignBit())
+                return getZeroExtendExpr(getAddExpr(Z0, getConstant(Trunc)),
+                                         UTy);
             }
     }
     break;

Modified: llvm/trunk/test/Analysis/ScalarEvolution/xor-and.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/xor-and.ll?rev=73664&r1=73663&r2=73664&view=diff

==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/xor-and.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/xor-and.ll Wed Jun 17 19:00:20 2009
@@ -1,6 +1,7 @@
-; RUN: llvm-as < %s | opt -scalar-evolution -disable-output -analyze | grep {\\-->  %z}
+; RUN: llvm-as < %s | opt -scalar-evolution -disable-output -analyze \
+; RUN:   | grep {\\-->  (zext i4 (-8 + (trunc i64 (8 \\* %x) to i4)) to i64)}
 
-; ScalarEvolution shouldn't try to analyze %s into something like
+; ScalarEvolution shouldn't try to analyze %z into something like
 ;   -->  (zext i4 (-1 + (-1 * (trunc i64 (8 * %x) to i4))) to i64)
 
 define i64 @foo(i64 %x) {