[mips] Handle undef when extracting subregs from FP64 registers.

Summary:
This removes unnecessary instructions when extracting from an undefined register
and also fixes a crash for O32 when passing undef to a double argument in
held in integer registers.

Reviewers: vkalintiris

Subscribers: llvm-commits, zoran.jovanovic, petarj

Differential Revision: http://reviews.llvm.org/D13467

llvm-svn: 250039
diff --git a/llvm/test/CodeGen/Mips/llvm-ir/call.ll b/llvm/test/CodeGen/Mips/llvm-ir/call.ll
index 112ab8e..6c4f08d 100644
--- a/llvm/test/CodeGen/Mips/llvm-ir/call.ll
+++ b/llvm/test/CodeGen/Mips/llvm-ir/call.ll
@@ -6,6 +6,7 @@
 ; RUN: llc -march=mips   -mcpu=mips32r3 -enable-mips-tail-calls < %s | FileCheck %s -check-prefix=ALL -check-prefix=O32
 ; RUN: llc -march=mips   -mcpu=mips32r5 -enable-mips-tail-calls < %s | FileCheck %s -check-prefix=ALL -check-prefix=O32
 ; RUN: llc -march=mips   -mcpu=mips32r6 -enable-mips-tail-calls < %s | FileCheck %s -check-prefix=ALL -check-prefix=O32
+; RUN: llc -march=mips   -mcpu=mips32r6 -mattr=+fp64,+nooddspreg -enable-mips-tail-calls < %s | FileCheck %s -check-prefix=ALL -check-prefix=O32
 ; RUN: llc -march=mips64 -mcpu=mips4    -enable-mips-tail-calls < %s | FileCheck %s -check-prefix=ALL -check-prefix=N64
 ; RUN: llc -march=mips64 -mcpu=mips64   -enable-mips-tail-calls < %s | FileCheck %s -check-prefix=ALL -check-prefix=N64
 ; RUN: llc -march=mips64 -mcpu=mips64r2 -enable-mips-tail-calls < %s | FileCheck %s -check-prefix=ALL -check-prefix=N64
@@ -168,3 +169,16 @@
   %1 = tail call float %addr()
   ret float %1
 }
+
+; Check that passing undef as a double value doesn't cause machine code errors
+; for FP64.
+declare hidden void @undef_double(i32 %this, double %volume) unnamed_addr align 2
+
+define hidden void @thunk_undef_double(i32 %this, double %volume) unnamed_addr align 2 {
+; ALL-LABEL: thunk_undef_double:
+; O32: # implicit-def: A2
+; O32: # implicit-def: A3
+; ALL: jr $25
+  tail call void @undef_double(i32 undef, double undef) #8
+  ret void
+}