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Reapply r121905 (automatic synthesis of @llvm.sadd.with.overflow) with a fix for a bug that manifested itself

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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
This commit is contained in:
Owen Anderson 2010-12-17 18:08:00 +00:00
parent 31f3578b00
commit e63dda51c2
2 changed files with 100 additions and 0 deletions
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73
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -1657,6 +1657,79 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
Value *A = 0, *B = 0;
// Match the following pattern, which is a common idiom when writing
// overflow-safe integer arithmetic function. The source performs an
// addition in wider type, and explicitly checks for overflow using
// comparisons against INT_MIN and INT_MAX. Simplify this by using the
// sadd_with_overflow intrinsic.
// FIXME: This could probably be generalized to handle other overflow-safe
// operations if we worked out the formulas to compute the appropriate
// magic constants.
//
// INT64 : a, b, sum = a + b
// if sum < INT32_MIN || sum > INT_MAX then
// ...
// else
// ...
{
ConstantInt *CI2;
// I = icmp ugt (add (add A B) CI2) CI
if (I.getPredicate() == ICmpInst::ICMP_UGT &&
match(Op0, m_Add(m_Add(m_Value(A), m_Value(B)),
m_ConstantInt(CI2)))) {
const IntegerType *WideType = cast<IntegerType>(CI->getType());
unsigned WideWidth = WideType->getBitWidth();
unsigned NarrowWidth = WideWidth / 2;
const IntegerType *NarrowType =
IntegerType::get(CI->getContext(), NarrowWidth);
// NarrowAllOnes and NarrowSignBit are the magic constants used to
// perform an overflow check in the wider type: 0x00..00FF..FF and
// 0x00..0010..00 respectively, where the highest set bit in each is
// what would be the sign bit in the narrower type.
ConstantInt *NarrowAllOnes = cast<ConstantInt>(ConstantInt::get(WideType,
APInt::getAllOnesValue(NarrowWidth).zext(WideWidth)));
APInt SignBit(WideWidth, 0);
SignBit.setBit(NarrowWidth-1);
ConstantInt *NarrowSignBit =
cast<ConstantInt>(ConstantInt::get(WideType, SignBit));
if (CI == NarrowAllOnes && CI2 == NarrowSignBit) {
Module *M = I.getParent()->getParent()->getParent();
const Type *IntrinsicType = NarrowType;
Value *F = Intrinsic::getDeclaration(M, Intrinsic::sadd_with_overflow,
&IntrinsicType, 1);
BasicBlock *InitialBlock = Builder->GetInsertBlock();
BasicBlock::iterator InitialInsert = Builder->GetInsertPoint();
// If the pattern matches, truncate the inputs to the narrower type and
// use the sadd_with_overflow intrinsic to efficiently compute both the
// result and the overflow bit.
Instruction *OrigAdd =
cast<Instruction>(cast<Instruction>(I.getOperand(0))->getOperand(0));
Builder->SetInsertPoint(OrigAdd->getParent(),
BasicBlock::iterator(OrigAdd));
Value *TruncA = Builder->CreateTrunc(A, NarrowType, A->getName());
Value *TruncB = Builder->CreateTrunc(B, NarrowType, B->getName());
CallInst *Call = Builder->CreateCall2(F, TruncA, TruncB);
Value *Add = Builder->CreateExtractValue(Call, 0);
Value *ZExt = Builder->CreateZExt(Add, WideType);
// The inner add was the result of the narrow add, zero extended to the
// wider type. Replace it with the result computed by the intrinsic.
OrigAdd->replaceAllUsesWith(ZExt);
Builder->SetInsertPoint(InitialBlock, InitialInsert);
return ExtractValueInst::Create(Call, 1);
}
}
}
// (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B)
if (I.isEquality() && CI->isZero() &&
match(Op0, m_Sub(m_Value(A), m_Value(B)))) {

27
test/Transforms/InstCombine/overflow.ll Normal file
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@ -0,0 +1,27 @@
; RUN: opt -S -instcombine < %s | FileCheck %s
; <rdar://problem/8558713>
; CHECK: @test1
define i32 @test1(i32 %a, i32 %b) nounwind ssp {
entry:
; CHECK-NOT: sext
%conv = sext i32 %a to i64
%conv2 = sext i32 %b to i64
%add = add nsw i64 %conv2, %conv
%add.off = add i64 %add, 2147483648
; CHECK: llvm.sadd.with.overflow
%0 = icmp ugt i64 %add.off, 4294967295
br i1 %0, label %if.then, label %if.end
if.then:
%call = tail call i32 (...)* @throwAnExceptionOrWhatever() nounwind
br label %if.end
if.end:
; CHECK-NOT: trunc
%conv9 = trunc i64 %add to i32
; CHECK: ret i32
ret i32 %conv9
}
declare i32 @throwAnExceptionOrWhatever(...)