[llvm-commits] [llvm] r72010 - in /llvm/trunk: lib/Analysis/ScalarEvolution.cpp test/Analysis/ScalarEvolution/and-xor.ll

[Dan Gohman]

Author: djg
Date: Mon May 18 11:29:04 2009
New Revision: 72010

URL: http://llvm.org/viewvc/llvm-project?rev=72010&view=rev
Log:
Teach ScalarEvolution to recognize x^-1 in the case where non-demanded
bits have been stripped out by instcombine.

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

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=72010&r1=72009&r2=72010&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Mon May 18 11:29:04 2009
@@ -2203,6 +2203,19 @@
       // If the RHS of xor is -1, then this is a not operation.
       if (CI->isAllOnesValue())
         return getNotSCEV(getSCEV(U->getOperand(0)));
+
+      // Model xor(and(x, C), C) as and(~x, C), if C is a low-bits mask.
+      // This is a variant of the check for xor with -1, and it handles
+      // the case where instcombine has trimmed non-demanded bits out
+      // of an xor with -1.
+      if (BinaryOperator *BO = dyn_cast<BinaryOperator>(U->getOperand(0)))
+        if (ConstantInt *LCI = dyn_cast<ConstantInt>(BO->getOperand(1)))
+          if (BO->getOpcode() == Instruction::And &&
+              LCI->getValue() == CI->getValue())
+            if (const SCEVZeroExtendExpr *Z =
+                  dyn_cast<SCEVZeroExtendExpr>(getSCEV(U->getOperand(0))))
+              return getZeroExtendExpr(getNotSCEV(Z->getOperand()),
+                                       U->getType());
     }
     break;
 

Added: llvm/trunk/test/Analysis/ScalarEvolution/and-xor.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/and-xor.ll?rev=72010&view=auto

==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/and-xor.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/and-xor.ll Mon May 18 11:29:04 2009
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -scalar-evolution -analyze -disable-output \
+; RUN:   | grep {\\-->  (zext} | count 2
+
+define i32 @foo(i32 %x) {
+  %n = and i32 %x, 255
+  %y = xor i32 %n, 255
+  ret i32 %y
+}