[llvm-commits] [llvm] r107074 - in /llvm/trunk: lib/VMCore/ConstantFold.cpp test/Transforms/InstCombine/icmp.ll

[Dan Gohman]

Author: djg
Date: Mon Jun 28 16:30:07 2010
New Revision: 107074

URL: http://llvm.org/viewvc/llvm-project?rev=107074&view=rev
Log:
Constant fold x == undef to undef.

Modified:
    llvm/trunk/lib/VMCore/ConstantFold.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp.ll

Modified: llvm/trunk/lib/VMCore/ConstantFold.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/VMCore/ConstantFold.cpp?rev=107074&r1=107073&r2=107074&view=diff
==============================================================================
--- llvm/trunk/lib/VMCore/ConstantFold.cpp (original)
+++ llvm/trunk/lib/VMCore/ConstantFold.cpp Mon Jun 28 16:30:07 2010
@@ -1817,8 +1817,15 @@
     return Constant::getAllOnesValue(ResultTy);
 
   // Handle some degenerate cases first
-  if (isa<UndefValue>(C1) || isa<UndefValue>(C2))
+  if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
+    // For EQ and NE, we can always pick a value for the undef to make the
+    // predicate pass or fail, so we can return undef.
+    if (ICmpInst::isEquality(ICmpInst::Predicate(pred)))
+      return UndefValue::get(ResultTy);
+    // Otherwise, pick the same value as the non-undef operand, and fold
+    // it to true or false.
     return ConstantInt::get(ResultTy, CmpInst::isTrueWhenEqual(pred));
+  }
 
   // No compile-time operations on this type yet.
   if (C1->getType()->isPPC_FP128Ty())

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=107074&r1=107073&r2=107074&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Mon Jun 28 16:30:07 2010
@@ -131,3 +131,26 @@
 ; CHECK: ret i1 false
 }
 
+define i1 @test14(i8 %X) nounwind readnone {
+entry:
+        %cmp = icmp slt i8 undef, -128
+        ret i1 %cmp
+; CHECK: @test14
+; CHECK: ret i1 false
+}
+
+define i1 @test15() nounwind readnone {
+entry:
+        %cmp = icmp eq i8 undef, -128
+        ret i1 %cmp
+; CHECK: @test15
+; CHECK: ret i1 undef
+}
+
+define i1 @test16() nounwind readnone {
+entry:
+        %cmp = icmp ne i8 undef, -128
+        ret i1 %cmp
+; CHECK: @test16
+; CHECK: ret i1 undef
+}