From b7d5409ad292f54def13989d868f2536713d6ece Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Tue, 30 Jul 2013 21:01:36 +0000
Subject: [PATCH] isKnownToBeAPowerOfTwo: Strengthen isKnownToBeAPowerOfTwo's
 analysis on add instructions

Call into ComputeMaskedBits to figure out which bits are set on both add
operands and determine if the value is a power-of-two-or-zero or not.

llvm-svn: 187445
---
 llvm/lib/Analysis/ValueTracking.cpp     | 46 +++++++++++++++++++++------------
 llvm/test/Transforms/InstCombine/rem.ll | 32 +++++++++++++++++++++++
 2 files changed, 62 insertions(+), 16 deletions(-)

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 84a6346..4591af8 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -855,22 +855,36 @@ bool llvm::isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth) {
     return false;
   }
 
-  if (match(V, m_Add(m_Value(X), m_Value(Y))))
-    if (OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V))
-      if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
-        // Adding a power of two to the same power of two is a power of two or
-        // zero.
-        if (BinaryOperator *XBO = dyn_cast<BinaryOperator>(X))
-          if (XBO->getOpcode() == Instruction::And)
-            if (XBO->getOperand(0) == Y || XBO->getOperand(1) == Y)
-              if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
-                return true;
-        if (BinaryOperator *YBO = dyn_cast<BinaryOperator>(Y))
-          if (YBO->getOpcode() == Instruction::And)
-            if (YBO->getOperand(0) == X || YBO->getOperand(1) == X)
-              if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
-                return true;
-      }
+  // Adding a power-of-two or zero to the same power-of-two or zero yields
+  // either the original power-of-two, a larger power-of-two or zero.
+  if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
+    OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
+    if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
+      if (match(X, m_And(m_Specific(Y), m_Value())) ||
+          match(X, m_And(m_Value(), m_Specific(Y))))
+        if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
+          return true;
+      if (match(Y, m_And(m_Specific(X), m_Value())) ||
+          match(Y, m_And(m_Value(), m_Specific(X))))
+        if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
+          return true;
+
+      unsigned BitWidth = V->getType()->getScalarSizeInBits();
+      APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
+      ComputeMaskedBits(X, LHSZeroBits, LHSOneBits, 0, Depth);
+
+      APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
+      ComputeMaskedBits(Y, RHSZeroBits, RHSOneBits, 0, Depth);
+      // If i8 V is a power of two or zero:
+      //  ZeroBits: 1 1 1 0 1 1 1 1
+      // ~ZeroBits: 0 0 0 1 0 0 0 0
+      if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
+        // If OrZero isn't set, we cannot give back a zero result.
+        // Make sure either the LHS or RHS has a bit set.
+        if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
+          return true;
+    }
+  }
 
   // An exact divide or right shift can only shift off zero bits, so the result
   // is a power of two only if the first operand is a power of two and not
diff --git a/llvm/test/Transforms/InstCombine/rem.ll b/llvm/test/Transforms/InstCombine/rem.ll
index 9272f83..22fd90b 100644
--- a/llvm/test/Transforms/InstCombine/rem.ll
+++ b/llvm/test/Transforms/InstCombine/rem.ll
@@ -172,3 +172,35 @@ define i32 @test17(i32 %X) {
   %A = urem i32 1, %X
   ret i32 %A
 }
+
+define i32 @test18(i16 %x, i32 %y) {
+; CHECK: @test18
+; CHECK-NEXT: [[AND:%.*]] = and i16 %x, 4
+; CHECK-NEXT: [[EXT:%.*]] = zext i16 [[AND]] to i32
+; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i32 [[EXT]], 3
+; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[SHL]], 63
+; CHECK-NEXT: [[REM:%.*]] = and i32 [[XOR]], %y
+; CHECK-NEXT: ret i32 [[REM]]
+	%1 = and i16 %x, 4
+	%2 = icmp ne i16 %1, 0
+	%3 = select i1 %2, i32 32, i32 64
+	%4 = urem i32 %y, %3
+	ret i32 %4
+}
+
+define i32 @test19(i32 %x, i32 %y) {
+; CHECK: @test19
+; CHECK-NEXT: [[SHL1:%.*]] = shl i32 1, %x
+; CHECK-NEXT: [[SHL2:%.*]] = shl i32 1, %y
+; CHECK-NEXT: [[AND:%.*]] = and i32 [[SHL1]], [[SHL2]]
+; CHECK-NEXT: [[ADD:%.*]] = add i32 [[AND]], [[SHL1]]
+; CHECK-NEXT: [[SUB:%.*]] = add i32 [[ADD]], -1
+; CHECK-NEXT: [[REM:%.*]] = and i32 [[SUB]], %y
+; CHECK-NEXT: ret i32 [[REM]]
+	%A = shl i32 1, %x
+	%B = shl i32 1, %y
+	%C = and i32 %A, %B
+	%D = add i32 %C, %A
+	%E = urem i32 %y, %D
+	ret i32 %E
+}
-- 
2.7.4