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When turning (ashr(shl(x, n), n)) into sext(trunc(x)), the width of the 

type to truncate to should be the number of bits of the value that are
preserved, not the number that are clobbered with sign-extension.
This fixes regressions in ldecod.

llvm-svn: 69704
This commit is contained in:
Dan Gohman 2009-04-21 20:18:36 +00:00
parent a8e8bc24b3
commit e14efcc9f4
2 changed files with 30 additions and 1 deletions
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2
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -2015,7 +2015,7 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
if (Instruction *L = dyn_cast<Instruction>(U->getOperand(0)))
if (L->getOpcode() == Instruction::Shl &&
L->getOperand(1) == U->getOperand(1)) {
uint64_t Amt = CI->getZExtValue();
uint64_t Amt = getTypeSizeInBits(U->getType()) - CI->getZExtValue();
return
SE.getSignExtendExpr(SE.getTruncateExpr(getSCEV(L->getOperand(0)),
IntegerType::get(Amt)),

29
llvm/test/Analysis/ScalarEvolution/sext-inreg.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: llvm-as < %s | opt -analyze -scalar-evolution -disable-output \
; RUN: | grep {signextend \{0,+,199\}<bb> to i64} | count 2
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
target triple = "i386-apple-darwin9.6"
define i64 @foo(i64* nocapture %x, i64 %n) nounwind {
entry:
%t0 = icmp sgt i64 %n, 0 ; <i1> [#uses=1]
br i1 %t0, label %bb, label %return
bb: ; preds = %bb, %entry
%i.01 = phi i64 [ 0, %entry ], [ %indvar.next, %bb ] ; <i32> [#uses=2]
%t1 = shl i64 %i.01, 7 ; <i32> [#uses=1]
%t2 = ashr i64 %t1, 7 ; <i32> [#uses=1]
%s1 = shl i64 %i.01, 5 ; <i32> [#uses=1]
%s2 = ashr i64 %s1, 5 ; <i32> [#uses=1]
%t3 = getelementptr i64* %x, i64 %i.01 ; <i64*> [#uses=1]
store i64 0, i64* %t3, align 1
%indvar.next = add i64 %i.01, 199 ; <i32> [#uses=2]
%exitcond = icmp eq i64 %indvar.next, %n ; <i1> [#uses=1]
br i1 %exitcond, label %return, label %bb
return: ; preds = %bb, %entry
%p = phi i64 [ 0, %entry ], [ %t2, %bb ]
%q = phi i64 [ 0, %entry ], [ %s2, %bb ]
%v = xor i64 %p, %q
ret i64 %v
}