http://llvm.org/bugs/show_bug.cgi?id=2831
Summary: instcombine complicates expression, and also gets it
wrong!
Product: new-bugs
Version: unspecified
Platform: Other
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P2
Component: new bugs
AssignedTo: [EMAIL PROTECTED]
ReportedBy: [EMAIL PROTECTED]
CC: [email protected]
Running "opt -instcombine" on this testcase:
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-f80:32:32"
target triple = "i386-pc-linux-gnu"
define i32 @main(i32 %argc, i8** %argv) nounwind {
entry:
%0 = ptrtoint i8** %argv to i32 ; <i32> [#uses=1]
%1 = add i32 %0, 1 ; <i32> [#uses=1]
ret i32 %1
}
Turns it into:
define i32 @main(i32 %argc, i8** %argv) nounwind {
entry:
%argv1 = bitcast i8** %argv to i8* ; <i8*> [#uses=1]
%ctg2 = getelementptr i8* %argv1, i32 1 ; <i8*> [#uses=1]
%0 = ptrtoint i8* %ctg2 to i32 ; <i32> [#uses=1]
ret i32 %0
}
Not only is this more complicated, but overflow behaviour
is different: i32 overflow is well-defined, while gep overflow
is not (at least, I don't think it is...). So this transform
is wrong as well as silly.
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