[llvm] r223583 - InstSimplify: Optimize away useless unsigned comparisons

[David Majnemer]

Author: majnemer
Date: Sat Dec  6 04:51:40 2014
New Revision: 223583

URL: http://llvm.org/viewvc/llvm-project?rev=223583&view=rev
Log:
InstSimplify: Optimize away useless unsigned comparisons

Code like X < Y && Y == 0 should always be folded away to false.

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/lib/IR/ConstantFold.cpp
    llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=223583&r1=223582&r2=223583&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Sat Dec  6 04:51:40 2014
@@ -1443,12 +1443,57 @@ Value *llvm::SimplifyAShrInst(Value *Op0
                             RecursionLimit);
 }
 
+static Value *simplifyUnsignedRangeCheck(ICmpInst *ZeroICmp,
+                                         ICmpInst *UnsignedICmp, bool IsAnd) {
+  Value *X, *Y;
+
+  ICmpInst::Predicate EqPred;
+  if (!match(ZeroICmp, m_ICmp(EqPred, m_Value(Y), m_Zero())) &&
+      ICmpInst::isEquality(EqPred))
+    return nullptr;
+
+  ICmpInst::Predicate UnsignedPred;
+  if (match(UnsignedICmp, m_ICmp(UnsignedPred, m_Value(X), m_Specific(Y))) &&
+      ICmpInst::isUnsigned(UnsignedPred))
+    ;
+  else if (match(UnsignedICmp,
+                 m_ICmp(UnsignedPred, m_Value(Y), m_Specific(X))) &&
+           ICmpInst::isUnsigned(UnsignedPred))
+    UnsignedPred = ICmpInst::getSwappedPredicate(UnsignedPred);
+  else
+    return nullptr;
+
+  // X < Y && Y != 0  -->  X < Y
+  // X < Y || Y != 0  -->  Y != 0
+  if (UnsignedPred == ICmpInst::ICMP_ULT && EqPred == ICmpInst::ICMP_NE)
+    return IsAnd ? UnsignedICmp : ZeroICmp;
+
+  // X >= Y || Y != 0  -->  true
+  // X >= Y || Y == 0  -->  X >= Y
+  if (UnsignedPred == ICmpInst::ICMP_UGE && !IsAnd) {
+    if (EqPred == ICmpInst::ICMP_NE)
+      return getTrue(UnsignedICmp->getType());
+    return UnsignedICmp;
+  }
+
+  // X < Y && Y == 0  -->  false
+  if (UnsignedPred == ICmpInst::ICMP_ULT && EqPred == ICmpInst::ICMP_EQ &&
+      IsAnd)
+    return getFalse(UnsignedICmp->getType());
+
+  return nullptr;
+}
+
 // Simplify (and (icmp ...) (icmp ...)) to true when we can tell that the range
 // of possible values cannot be satisfied.
 static Value *SimplifyAndOfICmps(ICmpInst *Op0, ICmpInst *Op1) {
   ICmpInst::Predicate Pred0, Pred1;
   ConstantInt *CI1, *CI2;
   Value *V;
+
+  if (Value *X = simplifyUnsignedRangeCheck(Op0, Op1, /*IsAnd=*/true))
+    return X;
+
   if (!match(Op0, m_ICmp(Pred0, m_Add(m_Value(V), m_ConstantInt(CI1)),
                          m_ConstantInt(CI2))))
    return nullptr;
@@ -1602,6 +1647,10 @@ static Value *SimplifyOrOfICmps(ICmpInst
   ICmpInst::Predicate Pred0, Pred1;
   ConstantInt *CI1, *CI2;
   Value *V;
+
+  if (Value *X = simplifyUnsignedRangeCheck(Op0, Op1, /*IsAnd=*/false))
+    return X;
+
   if (!match(Op0, m_ICmp(Pred0, m_Add(m_Value(V), m_ConstantInt(CI1)),
                          m_ConstantInt(CI2))))
    return nullptr;

Modified: llvm/trunk/lib/IR/ConstantFold.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/ConstantFold.cpp?rev=223583&r1=223582&r2=223583&view=diff
==============================================================================
--- llvm/trunk/lib/IR/ConstantFold.cpp (original)
+++ llvm/trunk/lib/IR/ConstantFold.cpp Sat Dec  6 04:51:40 2014
@@ -1350,7 +1350,7 @@ static ICmpInst::Predicate areGlobalsPot
                                                       const GlobalValue *GV2) {
   // Don't try to decide equality of aliases.
   if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
-    if (!GV1->hasExternalWeakLinkage() || !GV2->hasExternalWeakLinkage())
+    if (!GV1->hasExternalWeakLinkage() && !GV2->hasExternalWeakLinkage())
       return ICmpInst::ICMP_NE;
   return ICmpInst::BAD_ICMP_PREDICATE;
 }

Modified: llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll?rev=223583&r1=223582&r2=223583&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll Sat Dec  6 04:51:40 2014
@@ -155,3 +155,51 @@ define i32 @neg_nuw(i32 %x) {
   ret i32 %neg
 ; CHECK: ret i32 0
 }
+
+define i1 @and_icmp1(i32 %x, i32 %y) {
+  %1 = icmp ult i32 %x, %y
+  %2 = icmp ne i32 %y, 0
+  %3 = and i1 %1, %2
+  ret i1 %3
+}
+; CHECK-LABEL: @and_icmp1(
+; CHECK: %[[cmp:.*]] = icmp ult i32 %x, %y
+; CHECK: ret i1 %[[cmp]]
+
+define i1 @and_icmp2(i32 %x, i32 %y) {
+  %1 = icmp ult i32 %x, %y
+  %2 = icmp eq i32 %y, 0
+  %3 = and i1 %1, %2
+  ret i1 %3
+}
+; CHECK-LABEL: @and_icmp2(
+; CHECK: ret i1 false
+
+define i1 @or_icmp1(i32 %x, i32 %y) {
+  %1 = icmp ult i32 %x, %y
+  %2 = icmp ne i32 %y, 0
+  %3 = or i1 %1, %2
+  ret i1 %3
+}
+; CHECK-LABEL: @or_icmp1(
+; CHECK: %[[cmp:.*]] = icmp ne i32 %y, 0
+; CHECK: ret i1 %[[cmp]]
+
+define i1 @or_icmp2(i32 %x, i32 %y) {
+  %1 = icmp uge i32 %x, %y
+  %2 = icmp ne i32 %y, 0
+  %3 = or i1 %1, %2
+  ret i1 %3
+}
+; CHECK-LABEL: @or_icmp2(
+; CHECK: ret i1 true
+
+define i1 @or_icmp3(i32 %x, i32 %y) {
+  %1 = icmp uge i32 %x, %y
+  %2 = icmp eq i32 %y, 0
+  %3 = or i1 %1, %2
+  ret i1 %3
+}
+; CHECK-LABEL: @or_icmp3(
+; CHECK: %[[cmp:.*]] = icmp uge i32 %x, %y
+; CHECK: ret i1 %[[cmp]]