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We do want to allow LoadPRE to perform LICM-like transformations: we already consider PHI nodes to be negligible for

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code size (making this transform code size neutral), and it allows us to hoist values out of loops, which is always
a good thing.

llvm-svn: 115205
This commit is contained in:
Owen Anderson 2010-09-30 20:53:04 +00:00
parent 603950c4af
commit 5adba2c2ff
2 changed files with 39 additions and 13 deletions
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13
lib/Transforms/Scalar/GVN.cpp
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@ -1545,19 +1545,6 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
assert(TmpBB);
LoadBB = TmpBB;
// If we have a repl set with LI itself in it, this means we have a loop where
// at least one of the values is LI. Since this means that we won't be able
// to eliminate LI even if we insert uses in the other predecessors, we will
// end up increasing code size. Reject this by scanning for LI.
for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) {
if (ValuesPerBlock[i].isSimpleValue() &&
ValuesPerBlock[i].getSimpleValue() == LI) {
// Skip cases where LI is the only definition, even for EnableFullLoadPRE.
if (!EnableFullLoadPRE || e == 1)
return false;
}
}
// FIXME: It is extremely unclear what this loop is doing, other than
// artificially restricting loadpre.
if (isSinglePred) {

39
test/Transforms/GVN/load-pre-licm.ll Normal file
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@ -0,0 +1,39 @@
; RUN: opt -S -gvn < %s | FileCheck %s
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-n8:16:32"
target triple = "i386-apple-darwin11.0.0"
@sortlist = external global [5001 x i32], align 4
define void @Bubble() nounwind noinline {
; CHECK: entry:
; CHECK-NEXT: %tmp7.pre = load i32
entry:
br label %while.body5
; CHECK: while.body5:
; CHECK: %tmp7 = phi i32
; CHECK-NOT: %tmp7 = load i32
while.body5:
%indvar = phi i32 [ 0, %entry ], [ %tmp6, %if.end ]
%tmp5 = add i32 %indvar, 2
%arrayidx9 = getelementptr [5001 x i32]* @sortlist, i32 0, i32 %tmp5
%tmp6 = add i32 %indvar, 1
%arrayidx = getelementptr [5001 x i32]* @sortlist, i32 0, i32 %tmp6
%tmp7 = load i32* %arrayidx, align 4
%tmp10 = load i32* %arrayidx9, align 4
%cmp11 = icmp sgt i32 %tmp7, %tmp10
br i1 %cmp11, label %if.then, label %if.end
; CHECK: if.then:
if.then:
store i32 %tmp10, i32* %arrayidx, align 4
store i32 %tmp7, i32* %arrayidx9, align 4
br label %if.end
if.end:
%exitcond = icmp eq i32 %tmp6, 100
br i1 %exitcond, label %while.end.loopexit, label %while.body5
while.end.loopexit:
ret void
}