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Multiply can be evaluated in a different type, so long as the target type has

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a smaller bitwidth.

llvm-svn: 46244
This commit is contained in:
Nick Lewycky 2008-01-22 05:08:48 +00:00
parent c964ccb2c4
commit 78780f175b
2 changed files with 21 additions and 0 deletions
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10
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -6512,6 +6512,15 @@ static bool CanEvaluateInDifferentType(Value *V, const IntegerType *Ty,
CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
NumCastsRemoved);
case Instruction::Mul:
break;
// A multiply can be truncated by truncating its operands.
return Ty->getBitWidth() < OrigTy->getBitWidth() &&
CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved) &&
CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
NumCastsRemoved);
case Instruction::Shl:
// If we are truncating the result of this SHL, and if it's a shift of a
// constant amount, we can always perform a SHL in a smaller type.
@ -6571,6 +6580,7 @@ Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty,
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:

11
test/Transforms/InstCombine/2008-01-21-MulTrunc.ll Normal file
View File

@ -0,0 +1,11 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | notcast
define i16 @test1(i16 %a) {
%tmp = zext i16 %a to i32 ; <i32> [#uses=2]
%tmp21 = lshr i32 %tmp, 8 ; <i32> [#uses=1]
%tmp5 = mul i32 %tmp, 5 ; <i32> [#uses=1]
%tmp.upgrd.32 = or i32 %tmp21, %tmp5 ; <i32> [#uses=1]
%tmp.upgrd.3 = trunc i32 %tmp.upgrd.32 to i16 ; <i16> [#uses=1]
ret i16 %tmp.upgrd.3
}