[llvm] r179386 - Simplify (A & ~B) in icmp if A is a power of 2

[David Majnemer]

Author: majnemer
Date: Fri Apr 12 12:25:07 2013
New Revision: 179386

URL: http://llvm.org/viewvc/llvm-project?rev=179386&view=rev
Log:
Simplify (A & ~B) in icmp if A is a power of 2

The transform will execute like so:
(A & ~B) == 0 --> (A & B) != 0
(A & ~B) != 0 --> (A & B) == 0

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=179386&r1=179385&r2=179386&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Fri Apr 12 12:25:07 2013
@@ -2669,6 +2669,15 @@ Instruction *InstCombiner::visitICmpInst
   }
 
   { Value *A, *B;
+    // Transform (A & ~B) == 0 --> (A & B) != 0
+    // and       (A & ~B) != 0 --> (A & B) == 0
+    // if A is a power of 2.
+    if (match(Op0, m_And(m_Value(A), m_Not(m_Value(B)))) &&
+        match(Op1, m_Zero()) && isKnownToBeAPowerOfTwo(A) && I.isEquality())
+      return new ICmpInst(I.getInversePredicate(),
+                          Builder->CreateAnd(A, B),
+                          Op1);
+
     // ~x < ~y --> y < x
     // ~x < cst --> ~cst < x
     if (match(Op0, m_Not(m_Value(A)))) {

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=179386&r1=179385&r2=179386&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Fri Apr 12 12:25:07 2013
@@ -938,3 +938,29 @@ define i1 @icmp_sub57_sge_sub20(i32 %x,
   %cmp = icmp sge i32 %1, %2
   ret i1 %cmp
 }
+
+; CHECK: @icmp_and_shl_neg_ne_0
+; CHECK-NEXT: [[SHL:%[a-z0-9]+]] = shl i32 1, %B
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[SHL]], %A
+; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp eq i32 [[AND]], 0
+; CHECK-NEXT: ret i1 [[CMP]]
+define i1 @icmp_and_shl_neg_ne_0(i32 %A, i32 %B) {
+  %neg = xor i32 %A, -1
+  %shl = shl i32 1, %B
+  %and = and i32 %shl, %neg
+  %cmp = icmp ne i32 %and, 0
+  ret i1 %cmp
+}
+
+; CHECK: @icmp_and_shl_neg_eq_0
+; CHECK-NEXT: [[SHL:%[a-z0-9]+]] = shl i32 1, %B
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[SHL]], %A
+; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ne i32 [[AND]], 0
+; CHECK-NEXT: ret i1 [[CMP]]
+define i1 @icmp_and_shl_neg_eq_0(i32 %A, i32 %B) {
+  %neg = xor i32 %A, -1
+  %shl = shl i32 1, %B
+  %and = and i32 %shl, %neg
+  %cmp = icmp eq i32 %and, 0
+  ret i1 %cmp
+}