recognize an unsigned add with overflow idiom into uadd.
This resolves a README entry and technically resolves PR4916,
but we still get poor code for the testcase in that PR because
GVN isn't CSE'ing uadd with add, filed as PR8817.
Previously we got:
_test7: ## @test7
addq %rsi, %rdi
cmpq %rdi, %rsi
movl $42, %eax
cmovaq %rsi, %rax
ret
Now we get:
_test7: ## @test7
addq %rsi, %rdi
movl $42, %eax
cmovbq %rsi, %rax
ret
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122182 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 86a0ed2..6c6d26c 100644
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -1648,7 +1648,7 @@
// Put the new code above the original add, in case there are any uses of the
// add between the add and the compare.
- Builder->SetInsertPoint(OrigAdd->getParent(), BasicBlock::iterator(OrigAdd));
+ Builder->SetInsertPoint(OrigAdd);
Value *TruncA = Builder->CreateTrunc(A, NewType, A->getName()+".trunc");
Value *TruncB = Builder->CreateTrunc(B, NewType, B->getName()+".trunc");
@@ -1664,6 +1664,35 @@
return ExtractValueInst::Create(Call, 1, "sadd.overflow");
}
+static Instruction *ProcessUAddIdiom(Instruction &I, Value *OrigAddV,
+ InstCombiner &IC) {
+ // Don't bother doing this transformation for pointers, don't do it for
+ // vectors.
+ if (!isa<IntegerType>(OrigAddV->getType())) return 0;
+
+ // If the add is a constant expr, then we don't bother transforming it.
+ Instruction *OrigAdd = dyn_cast<Instruction>(OrigAddV);
+ if (OrigAdd == 0) return 0;
+
+ Value *LHS = OrigAdd->getOperand(0), *RHS = OrigAdd->getOperand(1);
+
+ // Put the new code above the original add, in case there are any uses of the
+ // add between the add and the compare.
+ InstCombiner::BuilderTy *Builder = IC.Builder;
+ Builder->SetInsertPoint(OrigAdd);
+
+ Module *M = I.getParent()->getParent()->getParent();
+ const Type *Ty = LHS->getType();
+ Value *F = Intrinsic::getDeclaration(M, Intrinsic::uadd_with_overflow, &Ty,1);
+ CallInst *Call = Builder->CreateCall2(F, LHS, RHS, "uadd");
+ Value *Add = Builder->CreateExtractValue(Call, 0);
+
+ IC.ReplaceInstUsesWith(*OrigAdd, Add);
+
+ // The original icmp gets replaced with the overflow value.
+ return ExtractValueInst::Create(Call, 1, "uadd.overflow");
+}
+
Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
bool Changed = false;
@@ -1726,11 +1755,11 @@
}
unsigned BitWidth = 0;
- if (TD)
- BitWidth = TD->getTypeSizeInBits(Ty->getScalarType());
- else if (Ty->isIntOrIntVectorTy())
+ if (Ty->isIntOrIntVectorTy())
BitWidth = Ty->getScalarSizeInBits();
-
+ else if (TD) // Pointers require TD info to get their size.
+ BitWidth = TD->getTypeSizeInBits(Ty->getScalarType());
+
bool isSignBit = false;
// See if we are doing a comparison with a constant.
@@ -2225,6 +2254,22 @@
if (match(Op0, m_Not(m_Value(A))) &&
match(Op1, m_Not(m_Value(B))))
return new ICmpInst(I.getPredicate(), B, A);
+
+ // (a+b) <u a --> llvm.uadd.with.overflow.
+ // (a+b) <u b --> llvm.uadd.with.overflow.
+ if (I.getPredicate() == ICmpInst::ICMP_ULT &&
+ match(Op0, m_Add(m_Value(A), m_Value(B))) &&
+ (Op1 == A || Op1 == B))
+ if (Instruction *R = ProcessUAddIdiom(I, Op0, *this))
+ return R;
+
+ // a >u (a+b) --> llvm.uadd.with.overflow.
+ // b >u (a+b) --> llvm.uadd.with.overflow.
+ if (I.getPredicate() == ICmpInst::ICMP_UGT &&
+ match(Op1, m_Add(m_Value(A), m_Value(B))) &&
+ (Op0 == A || Op0 == B))
+ if (Instruction *R = ProcessUAddIdiom(I, Op1, *this))
+ return R;
}
if (I.isEquality()) {