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add a note from PR5313 

llvm-svn: 86146
This commit is contained in:
Chris Lattner 2009-11-05 18:19:19 +00:00
parent 4127b8ef97
commit 06c26d982e
1 changed files with 34 additions and 0 deletions
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34
llvm/lib/Target/README.txt
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@ -1229,6 +1229,40 @@ GCC PR33344 is a similar case.
//===---------------------------------------------------------------------===//
[PHI TRANSLATE INDEXED GEPs] PR5313
Load redundancy elimination for simple loop. This loop:
void append_text(const char* text,unsigned char * const io) {
while(*text)
*io=*text++;
}
Compiles to have a fully redundant load in the loop (%2):
define void @append_text(i8* nocapture %text, i8* nocapture %io) nounwind {
entry:
%0 = load i8* %text, align 1 ; <i8> [#uses=1]
%1 = icmp eq i8 %0, 0 ; <i1> [#uses=1]
br i1 %1, label %return, label %bb
bb: ; preds = %bb, %entry
%indvar = phi i32 [ 0, %entry ], [ %tmp, %bb ] ; <i32> [#uses=2]
%text_addr.04 = getelementptr i8* %text, i32 %indvar ; <i8*> [#uses=1]
%2 = load i8* %text_addr.04, align 1 ; <i8> [#uses=1]
store i8 %2, i8* %io, align 1
%tmp = add i32 %indvar, 1 ; <i32> [#uses=2]
%scevgep = getelementptr i8* %text, i32 %tmp ; <i8*> [#uses=1]
%3 = load i8* %scevgep, align 1 ; <i8> [#uses=1]
%4 = icmp eq i8 %3, 0 ; <i1> [#uses=1]
br i1 %4, label %return, label %bb
return: ; preds = %bb, %entry
ret void
}
//===---------------------------------------------------------------------===//
There are many load PRE testcases in testsuite/gcc.dg/tree-ssa/loadpre* in the
GCC testsuite. There are many pre testcases as ssa-pre-*.c