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Fix PR4748: don't fold gep(bitcast(x)) into bitcast(gep) when x

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is itself a bitcast.  Since we have gep(bitcast(bitcast(y))) in this
case, just wait for the two bitcasts to get zapped.  This prevents
instcombine from confusing some aliasing stuff, and allows it to
directly eliminate the load in the testcase.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80508 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2009-08-30 20:38:21 +00:00
parent 963f4ba826
commit 2de2319124
2 changed files with 28 additions and 0 deletions
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7
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -10896,6 +10896,13 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
if (Value *X = getBitCastOperand(PtrOp)) {
assert(isa<PointerType>(X->getType()) && "Must be cast from pointer");
// If the input bitcast is actually "bitcast(bitcast(x))", then we don't
// want to change the gep until the bitcasts are eliminated.
if (getBitCastOperand(X)) {
Worklist.AddValue(PtrOp);
return 0;
}
// Transform: GEP (bitcast [10 x i8]* X to [0 x i8]*), i32 0, ...
// into : GEP [10 x i8]* X, i32 0, ...
//

21
test/Transforms/InstCombine/getelementptr-2.ll Normal file
View File

@ -0,0 +1,21 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep load
; PR4748
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"
target triple = "i386-apple-darwin9"
%struct.B = type { double }
%struct.A = type { %struct.B, i32, i32 }
define i32 @_Z4funcv(%struct.A* %a) {
entry:
%g3 = getelementptr %struct.A* %a, i32 0, i32 1
store i32 10, i32* %g3, align 4
%g4 = getelementptr %struct.A* %a, i32 0, i32 0
%new_a = bitcast %struct.B* %g4 to %struct.A*
%g5 = getelementptr %struct.A* %new_a, i32 0, i32 1
%a_a = load i32* %g5, align 4
ret i32 %a_a
}