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Avoid illegal integer promotion in fastisel

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Stop folding constant adds into GEP when the type size doesn't match.
Otherwise, the adds' operands are effectively being promoted, changing the
conditions of an overflow.  Results are different when:

    sext(a) + sext(b) != sext(a + b)

Problem originally found on x86-64, but also fixed issues with ARM and PPC,
which used similar code.

<rdar://problem/15292280>

Patch by Duncan Exon Smith!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194840 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bob Wilson 2013-11-15 19:09:27 +00:00
parent 5cddda6d13
commit cc7052343e
8 changed files with 102 additions and 21 deletions
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9
include/llvm/CodeGen/FastISel.h
View File

@ -358,6 +358,15 @@ protected:
return 0;
}
/// \brief Check if \c Add is an add that can be safely folded into \c GEP.
///
/// \c Add can be folded into \c GEP if:
/// - \c Add is an add,
/// - \c Add's size matches \c GEP's,
/// - \c Add is in the same basic block as \c GEP, and
/// - \c Add has a constant operand.
bool canFoldAddIntoGEP(const User *GEP, const Value *Add);
private:
bool SelectBinaryOp(const User *I, unsigned ISDOpcode);

15
lib/CodeGen/SelectionDAG/FastISel.cpp
View File

@ -1571,4 +1571,19 @@ bool FastISel::tryToFoldLoad(const LoadInst *LI, const Instruction *FoldInst) {
return tryToFoldLoadIntoMI(User, RI.getOperandNo(), LI);
}
bool FastISel::canFoldAddIntoGEP(const User *GEP, const Value *Add) {
// Must be an add.
if (!isa<AddOperator>(Add))
return false;
// Type size needs to match.
if (TD.getTypeSizeInBits(GEP->getType()) !=
TD.getTypeSizeInBits(Add->getType()))
return false;
// Must be in the same basic block.
if (isa<Instruction>(Add) &&
FuncInfo.MBBMap[cast<Instruction>(Add)->getParent()] != FuncInfo.MBB)
return false;
// Must have a constant operand.
return isa<ConstantInt>(cast<AddOperator>(Add)->getOperand(1));
}

9
lib/Target/ARM/ARMFastISel.cpp
View File

@ -900,13 +900,8 @@ bool ARMFastISel::ARMComputeAddress(const Value *Obj, Address &Addr) {
TmpOffset += CI->getSExtValue() * S;
break;
}
if (isa<AddOperator>(Op) &&
(!isa<Instruction>(Op) ||
FuncInfo.MBBMap[cast<Instruction>(Op)->getParent()]
== FuncInfo.MBB) &&
isa<ConstantInt>(cast<AddOperator>(Op)->getOperand(1))) {
// An add (in the same block) with a constant operand. Fold the
// constant.
if (canFoldAddIntoGEP(U, Op)) {
// A compatible add with a constant operand. Fold the constant.
ConstantInt *CI =
cast<ConstantInt>(cast<AddOperator>(Op)->getOperand(1));
TmpOffset += CI->getSExtValue() * S;

9
lib/Target/PowerPC/PPCFastISel.cpp
View File

@ -336,13 +336,8 @@ bool PPCFastISel::PPCComputeAddress(const Value *Obj, Address &Addr) {
TmpOffset += CI->getSExtValue() * S;
break;
}
if (isa<AddOperator>(Op) &&
(!isa<Instruction>(Op) ||
FuncInfo.MBBMap[cast<Instruction>(Op)->getParent()]
== FuncInfo.MBB) &&
isa<ConstantInt>(cast<AddOperator>(Op)->getOperand(1))) {
// An add (in the same block) with a constant operand. Fold the
// constant.
if (canFoldAddIntoGEP(U, Op)) {
// A compatible add with a constant operand. Fold the constant.
ConstantInt *CI =
cast<ConstantInt>(cast<AddOperator>(Op)->getOperand(1));
TmpOffset += CI->getSExtValue() * S;

9
lib/Target/X86/X86FastISel.cpp
View File

@ -561,13 +561,8 @@ redo_gep:
Disp += CI->getSExtValue() * S;
break;
}
if (isa<AddOperator>(Op) &&
(!isa<Instruction>(Op) ||
FuncInfo.MBBMap[cast<Instruction>(Op)->getParent()]
== FuncInfo.MBB) &&
isa<ConstantInt>(cast<AddOperator>(Op)->getOperand(1))) {
// An add (in the same block) with a constant operand. Fold the
// constant.
if (canFoldAddIntoGEP(U, Op)) {
// A compatible add with a constant operand. Fold the constant.
ConstantInt *CI =
cast<ConstantInt>(cast<AddOperator>(Op)->getOperand(1));
Disp += CI->getSExtValue() * S;

18
test/CodeGen/ARM/fastisel-gep-promote-before-add.ll Normal file
View File

@ -0,0 +1,18 @@
; fastisel should not fold add with non-pointer bitwidth
; sext(a) + sext(b) != sext(a + b)
; RUN: llc -mtriple=armv7-apple-ios %s -O0 -o - | FileCheck %s
define zeroext i8 @gep_promotion(i8* %ptr) nounwind uwtable ssp {
entry:
%ptr.addr = alloca i8*, align 8
%add = add i8 64, 64 ; 0x40 + 0x40
%0 = load i8** %ptr.addr, align 8
; CHECK-LABEL: _gep_promotion:
; CHECK: ldrb {{r[0-9]+}}, {{\[r[0-9]+\]}}
%arrayidx = getelementptr inbounds i8* %0, i8 %add
%1 = load i8* %arrayidx, align 1
ret i8 %1
}

17
test/CodeGen/PowerPC/fastisel-gep-promote-before-add.ll Normal file
View File

@ -0,0 +1,17 @@
; fastisel should not fold add with non-pointer bitwidth
; sext(a) + sext(b) != sext(a + b)
; RUN: llc -mtriple=powerpc64-unknown-freebsd10.0 %s -O0 -o - | FileCheck %s
define zeroext i8 @gep_promotion(i8* %ptr) nounwind uwtable ssp {
entry:
%ptr.addr = alloca i8*, align 8
%add = add i8 64, 64 ; 0x40 + 0x40
%0 = load i8** %ptr.addr, align 8
; CHECK-LABEL: gep_promotion:
; CHECK: lbz {{[0-9]+}}, 0({{.*}})
%arrayidx = getelementptr inbounds i8* %0, i8 %add
%1 = load i8* %arrayidx, align 1
ret i8 %1
}

37
test/CodeGen/X86/fastisel-gep-promote-before-add.ll Normal file
View File

@ -0,0 +1,37 @@
; fastisel should not fold add with non-pointer bitwidth
; sext(a) + sext(b) != sext(a + b)
; RUN: llc -mtriple=x86_64-apple-darwin %s -O0 -o - | FileCheck %s
define zeroext i8 @gep_promotion(i8* %ptr) nounwind uwtable ssp {
entry:
%ptr.addr = alloca i8*, align 8
%add = add i8 64, 64 ; 0x40 + 0x40
%0 = load i8** %ptr.addr, align 8
; CHECK-LABEL: _gep_promotion:
; CHECK: movzbl ({{.*}})
%arrayidx = getelementptr inbounds i8* %0, i8 %add
%1 = load i8* %arrayidx, align 1
ret i8 %1
}
define zeroext i8 @gep_promotion_nonconst(i8 %i, i8* %ptr) nounwind uwtable ssp {
entry:
%i.addr = alloca i8, align 4
%ptr.addr = alloca i8*, align 8
store i8 %i, i8* %i.addr, align 4
store i8* %ptr, i8** %ptr.addr, align 8
%0 = load i8* %i.addr, align 4
; CHECK-LABEL: _gep_promotion_nonconst:
; CHECK: movzbl ({{.*}})
%xor = xor i8 %0, -128 ; %0 ^ 0x80
%add = add i8 %xor, -127 ; %xor + 0x81
%1 = load i8** %ptr.addr, align 8
%arrayidx = getelementptr inbounds i8* %1, i8 %add
%2 = load i8* %arrayidx, align 1
ret i8 %2
}