Added inst combine tarnsform for (1 << X) & C pattrens where C is (so…

…me PowerOf2 - 1)

This patch can handles following cases from http://nondot.org/sabre/LLVMNotes/InstCombine.txt
  "((1 << X) & 7) == 0" ==> "X > 2"
  "((1 << X) & 7) != 0" ==> "X < 3".

Differential Revision: http://reviews.llvm.org/D3678

llvm-svn: 210007

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -2540,7 +2540,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
       // bit is set.   If the comparison is against zero, then this is a check
       // to see if *that* bit is set.
       APInt Op0KnownZeroInverted = ~Op0KnownZero;
-      if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
+      if (~Op1KnownZero == 0) {
         // If the LHS is an AND with the same constant, look through it.
         Value *LHS = nullptr;
         ConstantInt *LHSC = nullptr;
@@ -2550,11 +2550,19 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
 
         // If the LHS is 1 << x, and we know the result is a power of 2 like 8,
         // then turn "((1 << x)&8) == 0" into "x != 3".
+        // or turn "((1 << x)&7) == 0" into "x > 2".
         Value *X = nullptr;
         if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
-          unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
-          return new ICmpInst(ICmpInst::ICMP_NE, X,
-                              ConstantInt::get(X->getType(), CmpVal));
+          APInt ValToCheck = Op0KnownZeroInverted;
+          if (ValToCheck.isPowerOf2()) {
+            unsigned CmpVal = ValToCheck.countTrailingZeros();
+            return new ICmpInst(ICmpInst::ICMP_NE, X,
+                                ConstantInt::get(X->getType(), CmpVal));
+          } else if ((++ValToCheck).isPowerOf2()) {
+            unsigned CmpVal = ValToCheck.countTrailingZeros() - 1;
+            return new ICmpInst(ICmpInst::ICMP_UGT, X,
+                                ConstantInt::get(X->getType(), CmpVal));
+          }
         }
 
         // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
@@ -2577,7 +2585,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
       // bit is set.   If the comparison is against zero, then this is a check
       // to see if *that* bit is set.
       APInt Op0KnownZeroInverted = ~Op0KnownZero;
-      if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
+      if (~Op1KnownZero == 0) {
         // If the LHS is an AND with the same constant, look through it.
         Value *LHS = nullptr;
         ConstantInt *LHSC = nullptr;
@@ -2587,11 +2595,19 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
 
         // If the LHS is 1 << x, and we know the result is a power of 2 like 8,
         // then turn "((1 << x)&8) != 0" into "x == 3".
+        // or turn "((1 << x)&7) != 0" into "x < 3".
         Value *X = nullptr;
         if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
-          unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
-          return new ICmpInst(ICmpInst::ICMP_EQ, X,
-                              ConstantInt::get(X->getType(), CmpVal));
+          APInt ValToCheck = Op0KnownZeroInverted;
+          if (ValToCheck.isPowerOf2()) {
+            unsigned CmpVal = ValToCheck.countTrailingZeros();
+            return new ICmpInst(ICmpInst::ICMP_EQ, X,
+                                ConstantInt::get(X->getType(), CmpVal));
+          } else if ((++ValToCheck).isPowerOf2()) {
+            unsigned CmpVal = ValToCheck.countTrailingZeros();
+            return new ICmpInst(ICmpInst::ICMP_ULT, X,
+                                ConstantInt::get(X->getType(), CmpVal));
+          }
         }
 
         // If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,

llvm/test/Transforms/InstCombine/icmp.ll

@@ -166,6 +166,14 @@ define i1 @test17(i32 %x) nounwind {
 ; CHECK-NEXT: %cmp = icmp ne i32 %x, 3
 }
 
+define i1 @test17a(i32 %x) nounwind {
+  %shl = shl i32 1, %x
+  %and = and i32 %shl, 7
+  %cmp = icmp eq i32 %and, 0
+  ret i1 %cmp
+; CHECK-LABEL: @test17a(
+; CHECK-NEXT: %cmp = icmp ugt i32 %x, 2
+}
 
 define i1 @test18(i32 %x) nounwind {
   %sh = lshr i32 8, %x
@@ -194,6 +202,15 @@ define i1 @test20(i32 %x) nounwind {
 ; CHECK-NEXT: %cmp = icmp eq i32 %x, 3
 }
 
+define i1 @test20a(i32 %x) nounwind {
+  %shl = shl i32 1, %x
+  %and = and i32 %shl, 7
+  %cmp = icmp ne i32 %and, 0
+  ret i1 %cmp
+; CHECK-LABEL: @test20a(
+; CHECK-NEXT: %cmp = icmp ult i32 %x, 3
+}
+
 define i1 @test21(i8 %x, i8 %y) {
 ; CHECK-LABEL: @test21(
 ; CHECK-NOT: or i8