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Reapply r121905 (automatic synthesis of @llvm.sadd.with.overflow) with a fix for a bug that manifested itself
on the DragonEgg self-host bot. Unfortunately, the testcase is pretty messy and doesn't reduce well due to interactions with other parts of InstCombine. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122072 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1657,6 +1657,79 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
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if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
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Value *A = 0, *B = 0;
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// Match the following pattern, which is a common idiom when writing
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// overflow-safe integer arithmetic function. The source performs an
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// addition in wider type, and explicitly checks for overflow using
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// comparisons against INT_MIN and INT_MAX. Simplify this by using the
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// sadd_with_overflow intrinsic.
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// FIXME: This could probably be generalized to handle other overflow-safe
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// operations if we worked out the formulas to compute the appropriate
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// magic constants.
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//
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// INT64 : a, b, sum = a + b
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// if sum < INT32_MIN || sum > INT_MAX then
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// ...
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// else
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// ...
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{
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ConstantInt *CI2;
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// I = icmp ugt (add (add A B) CI2) CI
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if (I.getPredicate() == ICmpInst::ICMP_UGT &&
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match(Op0, m_Add(m_Add(m_Value(A), m_Value(B)),
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m_ConstantInt(CI2)))) {
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const IntegerType *WideType = cast<IntegerType>(CI->getType());
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unsigned WideWidth = WideType->getBitWidth();
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unsigned NarrowWidth = WideWidth / 2;
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const IntegerType *NarrowType =
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IntegerType::get(CI->getContext(), NarrowWidth);
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// NarrowAllOnes and NarrowSignBit are the magic constants used to
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// perform an overflow check in the wider type: 0x00..00FF..FF and
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// 0x00..0010..00 respectively, where the highest set bit in each is
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// what would be the sign bit in the narrower type.
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ConstantInt *NarrowAllOnes = cast<ConstantInt>(ConstantInt::get(WideType,
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APInt::getAllOnesValue(NarrowWidth).zext(WideWidth)));
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APInt SignBit(WideWidth, 0);
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SignBit.setBit(NarrowWidth-1);
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ConstantInt *NarrowSignBit =
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cast<ConstantInt>(ConstantInt::get(WideType, SignBit));
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if (CI == NarrowAllOnes && CI2 == NarrowSignBit) {
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Module *M = I.getParent()->getParent()->getParent();
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const Type *IntrinsicType = NarrowType;
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Value *F = Intrinsic::getDeclaration(M, Intrinsic::sadd_with_overflow,
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&IntrinsicType, 1);
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BasicBlock *InitialBlock = Builder->GetInsertBlock();
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BasicBlock::iterator InitialInsert = Builder->GetInsertPoint();
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// If the pattern matches, truncate the inputs to the narrower type and
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// use the sadd_with_overflow intrinsic to efficiently compute both the
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// result and the overflow bit.
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Instruction *OrigAdd =
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cast<Instruction>(cast<Instruction>(I.getOperand(0))->getOperand(0));
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Builder->SetInsertPoint(OrigAdd->getParent(),
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BasicBlock::iterator(OrigAdd));
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Value *TruncA = Builder->CreateTrunc(A, NarrowType, A->getName());
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Value *TruncB = Builder->CreateTrunc(B, NarrowType, B->getName());
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CallInst *Call = Builder->CreateCall2(F, TruncA, TruncB);
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Value *Add = Builder->CreateExtractValue(Call, 0);
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Value *ZExt = Builder->CreateZExt(Add, WideType);
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// The inner add was the result of the narrow add, zero extended to the
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// wider type. Replace it with the result computed by the intrinsic.
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OrigAdd->replaceAllUsesWith(ZExt);
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Builder->SetInsertPoint(InitialBlock, InitialInsert);
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return ExtractValueInst::Create(Call, 1);
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}
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}
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}
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// (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B)
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if (I.isEquality() && CI->isZero() &&
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match(Op0, m_Sub(m_Value(A), m_Value(B)))) {
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27
test/Transforms/InstCombine/overflow.ll
Normal file
27
test/Transforms/InstCombine/overflow.ll
Normal file
@ -0,0 +1,27 @@
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; RUN: opt -S -instcombine < %s | FileCheck %s
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; <rdar://problem/8558713>
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; CHECK: @test1
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define i32 @test1(i32 %a, i32 %b) nounwind ssp {
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entry:
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; CHECK-NOT: sext
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%conv = sext i32 %a to i64
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%conv2 = sext i32 %b to i64
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%add = add nsw i64 %conv2, %conv
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%add.off = add i64 %add, 2147483648
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; CHECK: llvm.sadd.with.overflow
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%0 = icmp ugt i64 %add.off, 4294967295
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br i1 %0, label %if.then, label %if.end
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if.then:
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%call = tail call i32 (...)* @throwAnExceptionOrWhatever() nounwind
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br label %if.end
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if.end:
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; CHECK-NOT: trunc
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%conv9 = trunc i64 %add to i32
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; CHECK: ret i32
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ret i32 %conv9
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}
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declare i32 @throwAnExceptionOrWhatever(...)
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