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Arnold Schwaighofer 0d2a656327 SimplifyCFG: Don't convert phis into selects if we could remove undef behavior 
instead

We used to transform this:

  define void @test6(i1 %cond, i8* %ptr) {
  entry:
    br i1 %cond, label %bb1, label %bb2

  bb1:
    br label %bb2

  bb2:
    %ptr.2 = phi i8* [ %ptr, %entry ], [ null, %bb1 ]
    store i8 2, i8* %ptr.2, align 8
    ret void
  }

into this:

  define void @test6(i1 %cond, i8* %ptr) {
    %ptr.2 = select i1 %cond, i8* null, i8* %ptr
    store i8 2, i8* %ptr.2, align 8
    ret void
  }

because the simplifycfg transformation into selects would happen to happen
before the simplifycfg transformation that removes unreachable control flow
(We have 'unreachable control flow' due to the store to null which is undefined
behavior).

The existing transformation that removes unreachable control flow in simplifycfg
is:

  /// If BB has an incoming value that will always trigger undefined behavior
  /// (eg. null pointer dereference), remove the branch leading here.
  static bool removeUndefIntroducingPredecessor(BasicBlock *BB)

Now we generate:

  define void @test6(i1 %cond, i8* %ptr) {
    store i8 2, i8* %ptr.2, align 8
    ret void
  }

I did not see any impact on the test-suite + externals.

rdar://18596215

llvm-svn: 219462
2014-10-10 01:27:02 +00:00
..
Hello [CMake] Add LLVM_LINK_COMPONENTS to loadable modules, LLVMHello and BugpointPasses, on Win32. 2014-07-13 13:36:48 +00:00
InstCombine [InstCombine] Fix wrong folding of constant comparisons involving ashr and negative values. 2014-10-09 12:41:49 +00:00
Instrumentation Use triple's isiOS() and isOSDarwin() methods. 2014-10-09 05:43:30 +00:00
IPO Inliner: Non-local functions in COMDATs shouldn't be dropped 2014-10-08 19:32:32 +00:00
ObjCARC Simplify creation of a bunch of ArrayRefs by using None, makeArrayRef or just letting them be implicitly created. 2014-08-27 05:25:25 +00:00
Scalar [Reassociate] Don't canonicalize X - undef to X + (-undef). 2014-10-09 20:06:29 +00:00
Utils SimplifyCFG: Don't convert phis into selects if we could remove undef behavior 2014-10-10 01:27:02 +00:00
Vectorize Rename getMaximumUnrollFactor -> getMaxInterleaveFactor; also rename option names controlling this variable. 2014-09-10 17:58:16 +00:00
CMakeLists.txt Extracted ObjCARC.cpp into its own library libLLVMObjCARCOpts in preparation for refactoring the ARC Optimizer. 2013-01-28 01:35:51 +00:00
LLVMBuild.txt Extracted ObjCARC.cpp into its own library libLLVMObjCARCOpts in preparation for refactoring the ARC Optimizer. 2013-01-28 01:35:51 +00:00
Makefile Extracted ObjCARC.cpp into its own library libLLVMObjCARCOpts in preparation for refactoring the ARC Optimizer. 2013-01-28 01:35:51 +00:00