Chris Lattner
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f50aa6ae5c
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Implement rdar://6480391, extending of equality icmp's to avoid a truncation.
I noticed this in the code compiled for a routine using std::map, which produced
this code:
%25 = tail call i32 @memcmp(i8* %24, i8* %23, i32 6) nounwind readonly
%.lobit.i = lshr i32 %25, 31 ; <i32> [#uses=1]
%tmp.i = trunc i32 %.lobit.i to i8 ; <i8> [#uses=1]
%toBool = icmp eq i8 %tmp.i, 0 ; <i1> [#uses=1]
br i1 %toBool, label %bb3, label %bb4
which compiled to:
call L_memcmp$stub
shrl $31, %eax
testb %al, %al
jne LBB1_11 ##
with this change, we compile it to:
call L_memcmp$stub
testl %eax, %eax
js LBB1_11
This triggers all the time in common code, with patters like this:
%169 = and i32 %ply, 1 ; <i32> [#uses=1]
%170 = trunc i32 %169 to i8 ; <i8> [#uses=1]
%toBool = icmp ne i8 %170, 0 ; <i1> [#uses=1]
%7 = lshr i32 %6, 24 ; <i32> [#uses=1]
%9 = trunc i32 %7 to i8 ; <i8> [#uses=1]
%10 = icmp ne i8 %9, 0 ; <i1> [#uses=1]
etc
llvm-svn: 61985
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2009-01-09 07:47:06 +00:00 |