[llvm-commits] [llvm] r151691 - /llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

[Bill Wendling]

Author: void
Date: Tue Feb 28 19:46:50 2012
New Revision: 151691

URL: http://llvm.org/viewvc/llvm-project?rev=151691&view=rev
Log:
Restrict this transformation to equality conditions.

This transformation is not correct for not-equal conditions:

(trunc x) != C1 & (and x, CA) != C2 -> (and x, CA|CMAX) != C1|C2

Let
  C1 == 0
  C2 == 0
  CA == 0xFF0000
  CMAX == 0xFF
and truncating to i8.

The original truth table:

    x   | A: trunc x != 0 | B: x & 0xFF0000 != 0 | A & B != 0
--------------------------------------------------------------
0x00000 |        0        |          0           |     0
0x00001 |        1        |          0           |     0
0x10000 |        0        |          1           |     0
0x10001 |        1        |          1           |     1

The truth table of the replacement:

    x   | x & 0xFF00FF != 0
----------------------------
0x00000 |        0
0x00001 |        1
0x10000 |        1
0x10001 |        1

So they are different.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=151691&r1=151690&r2=151691&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Tue Feb 28 19:46:50 2012
@@ -753,7 +753,7 @@
   // (trunc x) == C1 & (and x, CA) == C2 -> (and x, CA|CMAX) == C1|C2
   // where CMAX is the all ones value for the truncated type,
   // iff the lower bits of C2 and CA are zero.
-  if (LHSCC == RHSCC && ICmpInst::isEquality(LHSCC) &&
+  if (LHSCC == ICmpInst::ICMP_EQ && LHSCC == RHSCC &&
       LHS->hasOneUse() && RHS->hasOneUse()) {
     Value *V;
     ConstantInt *AndCst, *SmallCst = 0, *BigCst = 0;