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Improve constant folding of undef for binary operators. 

llvm-svn: 134221
This commit is contained in:
Dan Gohman 2011-07-01 00:42:17 +00:00
parent c011d31543
commit ca8d9e1341
2 changed files with 123 additions and 4 deletions
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28
llvm/lib/VMCore/ConstantFold.cpp
View File

@ -1014,20 +1014,38 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
case Instruction::Add:
case Instruction::Sub:
return UndefValue::get(C1->getType());
case Instruction::Mul:
case Instruction::And:
if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) // undef & undef -> undef
return C1;
return Constant::getNullValue(C1->getType()); // undef & X -> 0
case Instruction::Mul: {
ConstantInt *CI;
// X * undef -> undef if X is odd or undef
if (((CI = dyn_cast<ConstantInt>(C1)) && CI->getValue()[0]) ||
((CI = dyn_cast<ConstantInt>(C2)) && CI->getValue()[0]) ||
(isa<UndefValue>(C1) && isa<UndefValue>(C2)))
return UndefValue::get(C1->getType());
// X * undef -> 0 otherwise
return Constant::getNullValue(C1->getType());
}
case Instruction::UDiv:
case Instruction::SDiv:
// undef / 1 -> undef
if (Opcode == Instruction::UDiv || Opcode == Instruction::SDiv)
if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2))
if (CI2->isOne())
return C1;
// FALL THROUGH
case Instruction::URem:
case Instruction::SRem:
if (!isa<UndefValue>(C2)) // undef / X -> 0
return Constant::getNullValue(C1->getType());
return C2; // X / undef -> undef
case Instruction::Or: // X | undef -> -1
if (const VectorType *PTy = dyn_cast<VectorType>(C1->getType()))
return Constant::getAllOnesValue(PTy);
return Constant::getAllOnesValue(C1->getType());
if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) // undef | undef -> undef
return C1;
return Constant::getAllOnesValue(C1->getType()); // undef | X -> ~0
case Instruction::LShr:
if (isa<UndefValue>(C2) && isa<UndefValue>(C1))
return C1; // undef lshr undef -> undef
@ -1041,6 +1059,8 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
else
return C1; // X ashr undef --> X
case Instruction::Shl:
if (isa<UndefValue>(C2) && isa<UndefValue>(C1))
return C1; // undef shl undef -> undef
// undef << X -> 0 or X << undef -> 0
return Constant::getNullValue(C1->getType());
}

99
llvm/test/Transforms/InstSimplify/binop.ll Normal file
View File

@ -0,0 +1,99 @@
; RUN: opt -instsimplify -S < %s | FileCheck %s
; @test0
; CHECK: ret i64 undef
define i64 @test0() {
%r = mul i64 undef, undef
ret i64 %r
}
; @test1
; CHECK: ret i64 undef
define i64 @test1() {
%r = mul i64 3, undef
ret i64 %r
}
; @test2
; CHECK: ret i64 undef
define i64 @test2() {
%r = mul i64 undef, 3
ret i64 %r
}
; @test3
; CHECK: ret i64 0
define i64 @test3() {
%r = mul i64 undef, 6
ret i64 %r
}
; @test4
; CHECK: ret i64 0
define i64 @test4() {
%r = mul i64 6, undef
ret i64 %r
}
; @test5
; CHECK: ret i64 undef
define i64 @test5() {
%r = and i64 undef, undef
ret i64 %r
}
; @test6
; CHECK: ret i64 undef
define i64 @test6() {
%r = or i64 undef, undef
ret i64 %r
}
; @test7
; CHECK: ret i64 undef
define i64 @test7() {
%r = udiv i64 undef, 1
ret i64 %r
}
; @test8
; CHECK: ret i64 undef
define i64 @test8() {
%r = sdiv i64 undef, 1
ret i64 %r
}
; @test9
; CHECK: ret i64 0
define i64 @test9() {
%r = urem i64 undef, 1
ret i64 %r
}
; @test10
; CHECK: ret i64 0
define i64 @test10() {
%r = srem i64 undef, 1
ret i64 %r
}
; @test11
; CHECK: ret i64 undef
define i64 @test11() {
%r = shl i64 undef, undef
ret i64 %r
}
; @test12
; CHECK: ret i64 undef
define i64 @test12() {
%r = ashr i64 undef, undef
ret i64 %r
}
; @test13
; CHECK: ret i64 undef
define i64 @test13() {
%r = lshr i64 undef, undef
ret i64 %r
}