[PATCH] [InstCombineCompares] Added shl optimization for the instruction - icmp eq/ne (shl Const2, A), Const1

[David Majnemer]

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:1145
@@ +1144,3 @@
+  if (!AP1) {
+    unsigned zeros = AP2.countTrailingZeros();
+
----------------
This should be named Zeros.  Also, please reuse this for the calculation on line 1158.

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:1147-1150
@@ +1146,6 @@
+
+    if (zeros != 0) {
+      return getICmp(I.ICMP_UGE, A,
+                     ConstantInt::get(A->getType(), AP2.getBitWidth() - zeros));
+    }
+  }
----------------
I'd remove the braces around this.

================
Comment at: lib/Transforms/InstCombine/InstCombineCompares.cpp:1153-1164
@@ +1152,14 @@
+
+  if (AP1 == AP2) {
+    return getICmp(I.ICMP_EQ, A, ConstantInt::getNullValue(A->getType()));
+  }
+
+  // Get the distance between the lowest bits that are set.
+  int Shift = AP1.countTrailingZeros() - AP2.countTrailingZeros();
+
+  if (Shift > 0) {
+    if (AP2.shl(Shift) == AP1) {
+      return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));
+    }
+  }
+
----------------
These cases can be merged:
  if (Shift >= 0 && AP2.shl(Shift) == AP1)
    return getICmp(I.ICMP_EQ, A, ConstantInt::get(A->getType(), Shift));

http://reviews.llvm.org/D5839