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teach the truncation optimization that an entire chain of

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computation can be truncated if it is fed by a sext/zext that doesn't
have to be exactly equal to the truncation result type.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112285 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-08-27 20:32:06 +00:00
parent e8ac3f3be4
commit f9d05ab007
2 changed files with 26 additions and 4 deletions
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5
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@ -396,6 +396,11 @@ static bool CanEvaluateTruncated(Value *V, const Type *Ty) {
case Instruction::Trunc:
// trunc(trunc(x)) -> trunc(x)
return true;
case Instruction::ZExt:
case Instruction::SExt:
// trunc(ext(x)) -> ext(x) if the source type is smaller than the new dest
// trunc(ext(x)) -> trunc(x) if the source type is larger than the new dest
return true;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
return CanEvaluateTruncated(SI->getTrueValue(), Ty) &&

25
test/Transforms/InstCombine/trunc.ll
View File

@ -1,4 +1,5 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
; Instcombine should be able to eliminate all of these ext casts.
@ -76,7 +77,23 @@ define i92 @test7(i64 %A) {
%D = trunc i128 %C to i92
ret i92 %D
; CHECK: @test7
; CHECK: %C = lshr i64 %A, 32
; CHECK: %D = zext i64 %C to i92
; CHECK: ret i92 %D
}
; CHECK: %B = zext i64 %A to i92
; CHECK: %C = lshr i92 %B, 32
; CHECK: ret i92 %C
}
define i64 @test8(i32 %A, i32 %B) {
%tmp38 = zext i32 %A to i128
%tmp32 = zext i32 %B to i128
%tmp33 = shl i128 %tmp32, 32
%ins35 = or i128 %tmp33, %tmp38
%tmp42 = trunc i128 %ins35 to i64
ret i64 %tmp42
; CHECK: @test8
; CHECK: %tmp38 = zext i32 %A to i64
; CHECK: %tmp32 = zext i32 %B to i64
; CHECK: %tmp33 = shl i64 %tmp32, 32
; CHECK: %ins35 = or i64 %tmp33, %tmp38
; CHECK: ret i64 %ins35
}