Index: lib/Target/X86/X86InstrCompiler.td =================================================================== --- lib/Target/X86/X86InstrCompiler.td +++ lib/Target/X86/X86InstrCompiler.td @@ -1191,6 +1191,7 @@ return N->getOpcode() != ISD::TRUNCATE && N->getOpcode() != TargetOpcode::EXTRACT_SUBREG && N->getOpcode() != ISD::CopyFromReg && + N->getOpcode() != ISD::AssertSext && N->getOpcode() != X86ISD::CMOV; }]>; Index: test/CodeGen/X86/TruncAssertZext.ll =================================================================== --- test/CodeGen/X86/TruncAssertZext.ll +++ test/CodeGen/X86/TruncAssertZext.ll @@ -0,0 +1,15 @@ +; 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 %ecx, %eax + %or = or i64 %a, -2 + %trunc = trunc i64 %or to i32 + br label %l +l: + %ext = zext i32 %trunc to i64 + ret i64 %ext +} \ No newline at end of file