missing instcombine for GEP 0,X,Y,Z of bitcast of Ty* to [0 x Ty]*

[llvmbot]

Bugzilla Link	3694
Resolution	FIXED
Resolved on	Mar 02, 2009 06:39
Version	unspecified
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@nlewycky

Extended Description

test/FrontendC/2007-03-27-VarLengthArray.c now compiles to

define i32 @​e(i32 %m, i32 %n) nounwind {
entry:
%0 = alloca i32, i32 %n, align 4 ; <i32*> [#uses=2]
%1 = bitcast i32* %0 to [0 x i32]* ; <[0 x i32]> [#uses=1]
call void @​f(i32 %0) nounwind
%2 = getelementptr [0 x i32]* %1, i32 0, i32 %m ; <i32*> [#uses=1]
%3 = load i32* %2, align 4 ; [#uses=1]
ret i32 %3
}

The bitcast could be eliminated by stripping the
first index off the GEP.

[lattner]

For specific instcombine micro optimizations, we generally prefer to put them in lib/target/readme.txt, unless this represents a major win for some specific use-case.

[llvmbot]

Fixed here:
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20090302/074464.html