[X86] Fix pattern match for 32-to-64-bit zext in the presence of AssertSext

This fixes an issue with matching trunc -> assertsext -> zext on x86-64, which would not zero the high 32-bits. See PR20494 for details.
Recommitting - This time, with a hopefully working test.

Differential Revision: http://reviews.llvm.org/D6128

llvm-svn: 221672

llvm/lib/Target/X86/X86InstrCompiler.td

@@ -1191,6 +1191,7 @@ def def32 : PatLeaf<(i32 GR32:$src), [{
   return N->getOpcode() != ISD::TRUNCATE &&
          N->getOpcode() != TargetOpcode::EXTRACT_SUBREG &&
          N->getOpcode() != ISD::CopyFromReg &&
+         N->getOpcode() != ISD::AssertSext &&
          N->getOpcode() != X86ISD::CMOV;
 }]>;
 

llvm/test/CodeGen/X86/TruncAssertZext.ll

@@ -0,0 +1,16 @@
+; RUN: llc < %s -O2 -march=x86-64 | FileCheck %s
+; Checks that a zeroing mov is inserted for the trunc/zext pair even when
+; the source of the zext is an AssertSext node
+; PR20494
+
+define i64 @main(i64 %a) { 
+; CHECK-LABEL: main
+; CHECK: movl %e{{..}}, %eax
+; CHECK: ret
+  %or = or i64 %a, -2
+  %trunc = trunc i64 %or to i32
+  br label %l
+l:
+  %ext = zext i32 %trunc to i64
+  ret i64 %ext
+}