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Fix assertion failure in global-merge with unused ConstantExpr

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The global-merge pass was crashing because it assumes that all ConstantExprs
(reached via the global variables that they use) have at least one user.

I haven't worked out a way to test this, as an unused ConstantExpr cannot be
represented by serialised IR, and global-merge can only be run in llc, which
does not run any passes which can make a ConstantExpr dead.

This (reduced to the point of silliness) C code triggers this bug when compiled
for arm-none-eabi at -O1:

  static a = 7;
  static volatile b[10] = {&a};

  c;
  main() {
    c = 0;
    for (; c < 10;)
      printf(b[c]);
  }

Differential Revision: http://reviews.llvm.org/D10314



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239308 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Oliver Stannard 2015-06-08 16:55:31 +00:00
parent 838271c858
commit 7c40b1a7bc
1 changed files with 2 additions and 0 deletions
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2
lib/CodeGen/GlobalMerge.cpp
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@ -280,6 +280,8 @@ bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
// users, so look through ConstantExpr...
Use *UI, *UE;
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U.getUser())) {
if (CE->use_empty())
continue;
UI = &*CE->use_begin();
UE = nullptr;
} else if (isa<Instruction>(U.getUser())) {