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ConstantFold: Fix big shift constant folding 

Constant folding for shift IR instructions ignores all bits above 32 of
second argument (shift amount).
Because of that, some undef results are not recognized and APInt can
raise an assert failure if second argument has more than 64 bits.

Patch by Paweł Bylica!

Differential Revision: http://reviews.llvm.org/D7701

llvm-svn: 232176
This commit is contained in:
David Majnemer 2015-03-13 16:39:46 +00:00
parent d3b7582c84
commit e2a4b856d8
2 changed files with 81 additions and 21 deletions
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33
llvm/lib/IR/ConstantFold.cpp
View File

@ -1120,27 +1120,18 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
return ConstantInt::get(CI1->getContext(), C1V | C2V);
case Instruction::Xor:
return ConstantInt::get(CI1->getContext(), C1V ^ C2V);
case Instruction::Shl: {
uint32_t shiftAmt = C2V.getZExtValue();
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(CI1->getContext(), C1V.shl(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
case Instruction::LShr: {
uint32_t shiftAmt = C2V.getZExtValue();
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(CI1->getContext(), C1V.lshr(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
case Instruction::AShr: {
uint32_t shiftAmt = C2V.getZExtValue();
if (shiftAmt < C1V.getBitWidth())
return ConstantInt::get(CI1->getContext(), C1V.ashr(shiftAmt));
else
return UndefValue::get(C1->getType()); // too big shift is undef
}
case Instruction::Shl:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.shl(C2V));
return UndefValue::get(C1->getType()); // too big shift is undef
case Instruction::LShr:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.lshr(C2V));
return UndefValue::get(C1->getType()); // too big shift is undef
case Instruction::AShr:
if (C2V.ult(C1V.getBitWidth()))
return ConstantInt::get(CI1->getContext(), C1V.ashr(C2V));
return UndefValue::get(C1->getType()); // too big shift is undef
}
}

69
llvm/test/Transforms/ConstProp/shift.ll Normal file
View File

@ -0,0 +1,69 @@
; RUN: opt < %s -constprop -S | FileCheck %s
; CHECK-LABEL: shift_undef_64
define void @shift_undef_64(i64* %p) {
%r1 = lshr i64 -1, 4294967296 ; 2^32
; CHECK: store i64 undef
store i64 %r1, i64* %p
%r2 = ashr i64 -1, 4294967297 ; 2^32 + 1
; CHECK: store i64 undef
store i64 %r2, i64* %p
%r3 = shl i64 -1, 4294967298 ; 2^32 + 2
; CHECK: store i64 undef
store i64 %r3, i64* %p
ret void
}
; CHECK-LABEL: shift_undef_65
define void @shift_undef_65(i65* %p) {
%r1 = lshr i65 2, 18446744073709551617
; CHECK: store i65 undef
store i65 %r1, i65* %p
%r2 = ashr i65 4, 18446744073709551617
; CHECK: store i65 undef
store i65 %r2, i65* %p
%r3 = shl i65 1, 18446744073709551617
; CHECK: store i65 undef
store i65 %r3, i65* %p
ret void
}
; CHECK-LABEL: shift_undef_256
define void @shift_undef_256(i256* %p) {
%r1 = lshr i256 2, 18446744073709551617
; CHECK: store i256 undef
store i256 %r1, i256* %p
%r2 = ashr i256 4, 18446744073709551618
; CHECK: store i256 undef
store i256 %r2, i256* %p
%r3 = shl i256 1, 18446744073709551619
; CHECK: store i256 undef
store i256 %r3, i256* %p
ret void
}
; CHECK-LABEL: shift_undef_511
define void @shift_undef_511(i511* %p) {
%r1 = lshr i511 -1, 1208925819614629174706276 ; 2^80 + 100
; CHECK: store i511 undef
store i511 %r1, i511* %p
%r2 = ashr i511 -2, 1208925819614629174706200
; CHECK: store i511 undef
store i511 %r2, i511* %p
%r3 = shl i511 -3, 1208925819614629174706180
; CHECK: store i511 undef
store i511 %r3, i511* %p
ret void
}