Constant folding cast for zero vectors is missing

[llvmbot]

Bugzilla Link	9011
Resolution	FIXED
Resolved on	Jan 20, 2011 19:58
Version	trunk
OS	Windows NT
Reporter	LLVM Bugzilla Contributor

Extended Description

There is missing constant folding of casting operation for vector of 0's.
Probably it is due to fact that vector of zeroes is described by ConstantAggregateZero and its handling is missing from ConstantFolding.

As result some of the shaders when running with 'opt -std-compile-opts' may run infinitely long time. See attached .ll for example.

To reproduce the bug just run attached .ll with 'opt -std-compile-opts'

The fix is inlined (due to its simplicity)
Index: lib/VMCore/ConstantFold.cpp

--- lib/VMCore/ConstantFold.cpp (revision 2460)
+++ lib/VMCore/ConstantFold.cpp (working copy)
@@ -553,6 +553,9 @@
return ConstantVector::get(DestVecTy, res);
}

• if (ConstantAggregateZero *CZ = dyn_cast(V)) {

•  return Constant::getNullValue(DestTy);
  

• }
  // We actually have to do a cast now. Perform the cast according to the
  // opcode specified.
  switch (opc) {

[llvmbot]

Missing attachment...

[llvmbot]

Proposed tsetcase:

@​test1 = constant <4 x i32> zext (<4 x i8> zeroinitializer to <4 x i32>)
@​test2 = constant <4 x i32> sext (<4 x i8> zeroinitializer to <4 x i32>)
@​test3 = constant <4 x i32> bitcast (<16 x i8> zeroinitializer to <4 x i32>)
@​test4 = constant <4 x float> uitofp (<4 x i8> zeroinitializer to <4 x float>)
@​test5 = constant <4 x float> sitofp (<4 x i8> zeroinitializer to <4 x float>)
@​test6 = constant <4 x i32> fptosi (<4 x float> zeroinitializer to <4 x i32>)
@​test7 = constant <4 x i32> fptoui (<4 x float> zeroinitializer to <4 x i32>)
@​test8 = constant <4 x float> fptrunc (<4 x double> zeroinitializer to <4 x float>)
@​test9 = constant <4 x double> fpext (<4 x float> zeroinitializer to <4 x double>)

@​test10 = constant <4 x double> bitcast (i256 0 to <4 x double>)
@​test11 = constant <4 x float> bitcast (i128 0 to <4 x float>)
@​test12 = constant <4 x i32> bitcast (i128 0 to <4 x i32>)

as of today, only test3, 10, 11, 12 work.

[llvmbot]

Fixed in
http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110117/115540.html