From 7ddcd35d6beb99118f0b960329b304f9e9a2bf58 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Mon, 26 Mar 2012 01:44:11 +0000
Subject: [PATCH] Use the new range metadata in computeMaskedBits and add a new
 optimization to instruction simplify that lets us remove an and when loding a
 boolean value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153423 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/InstructionSimplify.cpp    | 15 ++++++++++++++
 lib/Analysis/ValueTracking.cpp          | 26 +++++++++++++++++++++++++
 test/Transforms/InstSimplify/pr12251.ll | 15 ++++++++++++++
 3 files changed, 56 insertions(+)
 create mode 100644 test/Transforms/InstSimplify/pr12251.ll

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 16e7a726595..28400b08b1c 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -1370,6 +1370,21 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const Query &Q,
       return Op1;
   }
 
+  unsigned Bitwidth = Op1->getType()->getScalarSizeInBits();
+  APInt DemandedMask = APInt::getAllOnesValue(Bitwidth);
+  APInt KnownZero0 = APInt::getNullValue(Bitwidth);
+  APInt KnownOne0 = APInt::getNullValue(Bitwidth);
+  ComputeMaskedBits(Op0, DemandedMask, KnownZero0, KnownOne0);
+  APInt KnownZero1 = APInt::getNullValue(Bitwidth);
+  APInt KnownOne1 = APInt::getNullValue(Bitwidth);
+  ComputeMaskedBits(Op1, DemandedMask, KnownZero1, KnownOne1);
+
+  if ((KnownZero0 | KnownOne1).isAllOnesValue())
+    return Op0;
+
+  if ((KnownZero1 | KnownOne0).isAllOnesValue())
+    return Op1;
+
   // Try some generic simplifications for associative operations.
   if (Value *V = SimplifyAssociativeBinOp(Instruction::And, Op0, Op1, Q,
                                           MaxRecurse))
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 01e00caa3b2..17bad941e50 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -20,8 +20,10 @@
 #include "llvm/GlobalAlias.h"
 #include "llvm/IntrinsicInst.h"
 #include "llvm/LLVMContext.h"
+#include "llvm/Metadata.h"
 #include "llvm/Operator.h"
 #include "llvm/Target/TargetData.h"
+#include "llvm/Support/ConstantRange.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/PatternMatch.h"
@@ -195,6 +197,26 @@ static void ComputeMaskedBitsMul(Value *Op0, Value *Op1, bool NSW,
     KnownOne.setBit(BitWidth - 1);
 }
 
+static void computeMaskedBitsLoad(const MDNode &Ranges, const APInt &Mask,
+                                  APInt &KnownZero) {
+  unsigned BitWidth = Mask.getBitWidth();
+  unsigned NumRanges = Ranges.getNumOperands() / 2;
+  assert(NumRanges >= 1);
+
+  // Use the high end of the ranges to find leading zeros.
+  unsigned MinLeadingZeros = BitWidth;
+  for (unsigned i = 0; i < NumRanges; ++i) {
+    ConstantInt *Lower = cast<ConstantInt>(Ranges.getOperand(2*i + 0));
+    ConstantInt *Upper = cast<ConstantInt>(Ranges.getOperand(2*i + 1));
+    ConstantRange Range(Lower->getValue(), Upper->getValue());
+    if (Range.isWrappedSet())
+      MinLeadingZeros = 0; // -1 has no zeros
+    unsigned LeadingZeros = (Upper->getValue() - 1).countLeadingZeros();
+    MinLeadingZeros = std::min(LeadingZeros, MinLeadingZeros);
+  }
+
+  KnownZero = Mask & APInt::getHighBitsSet(BitWidth, MinLeadingZeros);
+}
 /// ComputeMaskedBits - Determine which of the bits specified in Mask are
 /// known to be either zero or one and return them in the KnownZero/KnownOne
 /// bit sets.  This code only analyzes bits in Mask, in order to short-circuit
@@ -315,6 +337,10 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
   APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
   switch (I->getOpcode()) {
   default: break;
+  case Instruction::Load:
+    if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
+      computeMaskedBitsLoad(*MD, Mask, KnownZero);
+    return;
   case Instruction::And: {
     // If either the LHS or the RHS are Zero, the result is zero.
     ComputeMaskedBits(I->getOperand(1), Mask, KnownZero, KnownOne, TD, Depth+1);
diff --git a/test/Transforms/InstSimplify/pr12251.ll b/test/Transforms/InstSimplify/pr12251.ll
new file mode 100644
index 00000000000..f180f9f1eba
--- /dev/null
+++ b/test/Transforms/InstSimplify/pr12251.ll
@@ -0,0 +1,15 @@
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+
+define zeroext i1 @_Z3fooPb(i8* nocapture %x) {
+entry:
+  %a = load i8* %x, align 1, !range !0
+  %b = and i8 %a, 1
+  %tobool = icmp ne i8 %b, 0
+  ret i1 %tobool
+}
+
+; CHECK: %a = load i8* %x, align 1, !range !0
+; CHECK-NEXT: %tobool = icmp ne i8 %a, 0
+; CHECK-NEXT: ret i1 %tobool
+
+!0 = metadata !{i8 0, i8 2}