The PowerPC VRSAVE register has been somewhat of an odd beast since

the Altivec extensions were introduced.  Its use is optional, and
allows the compiler to communicate to the operating system which
vector registers should be saved and restored during a context switch.
In practice, this information is ignored by the various operating
systems using the SVR4 ABI; the kernel saves and restores the entire
register state.  Setting the VRSAVE register is no longer performed by
the AIX XL compilers, the IBM i compilers, or by GCC on Power Linux
systems.  It seems best to avoid this logic within LLVM as well.

This patch avoids generating code to update and restore VRSAVE for the
PowerPC SVR4 ABIs (32- and 64-bit).  The code remains in place for the
Darwin ABI.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165656 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/PowerPC/PPCFrameLowering.cpp b/lib/Target/PowerPC/PPCFrameLowering.cpp
index b1c02e57f8866710cbd6faaaf590ae8bd2691b31..caf7bf2be793247dcbbc59767f3d693c296ac9eb 100644 (file)
--- a/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/lib/Target/PowerPC/PPCFrameLowering.cpp
@@ -50,6 +50,11 @@ static const uint16_t VRRegNo[] = {
 /// to manipulate the VRSAVE register, even though it uses vector registers.
 /// This can happen when the only registers used are known to be live in or out
 /// of the function.  Remove all of the VRSAVE related code from the function.
+/// FIXME: The removal of the code results in a compile failure at -O0 when the
+/// function contains a function call, as the GPR containing original VRSAVE
+/// contents is spilled and reloaded around the call.  Without the prolog code,
+/// the spill instruction refers to an undefined register.  This code needs
+/// to account for all uses of that GPR.
 static void RemoveVRSaveCode(MachineInstr *MI) {
   MachineBasicBlock *Entry = MI->getParent();
   MachineFunction *MF = Entry->getParent();
@@ -283,12 +288,13 @@ void PPCFrameLowering::emitPrologue(MachineFunction &MF) const {
 
   // Scan the prolog, looking for an UPDATE_VRSAVE instruction.  If we find it,
   // process it.
-  for (unsigned i = 0; MBBI != MBB.end(); ++i, ++MBBI) {
-    if (MBBI->getOpcode() == PPC::UPDATE_VRSAVE) {
-      HandleVRSaveUpdate(MBBI, TII);
-      break;
+  if (!Subtarget.isSVR4ABI())
+    for (unsigned i = 0; MBBI != MBB.end(); ++i, ++MBBI) {
+      if (MBBI->getOpcode() == PPC::UPDATE_VRSAVE) {
+        HandleVRSaveUpdate(MBBI, TII);
+        break;
+      }
     }
-  }
 
   // Move MBBI back to the beginning of the function.
   MBBI = MBB.begin();

diff --git a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index b52452ce89b6b2198432806634acd8b65a88e1c2..6195441cfc0d9cb5218e2dde25441f334ce9c3e4 100644 (file)
--- a/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
@@ -53,7 +53,9 @@ namespace {
       GlobalBaseReg = 0;
       SelectionDAGISel::runOnMachineFunction(MF);
 
-      InsertVRSaveCode(MF);
+      if (!PPCSubTarget.isSVR4ABI())
+        InsertVRSaveCode(MF);
+
       return true;
     }
 

diff --git a/test/CodeGen/PowerPC/novrsave.ll b/test/CodeGen/PowerPC/novrsave.ll
new file mode 100644 (file)
index 0000000..a70576a
--- /dev/null
+++ b/test/CodeGen/PowerPC/novrsave.ll
@@ -0,0 +1,15 @@
+; RUN: llc -O0 -mtriple=powerpc-unknown-linux-gnu   < %s | FileCheck %s
+; RUN: llc -O0 -mtriple=powerpc64-unknown-linux-gnu < %s | FileCheck %s
+
+; This verifies that the code to update VRSAVE has been removed for SVR4.
+
+define <4 x float> @bar(<4 x float> %v) nounwind {
+entry:
+  %v.addr = alloca <4 x float>, align 16
+  store <4 x float> %v, <4 x float>* %v.addr, align 16
+  %0 = load <4 x float>* %v.addr, align 16
+  ret <4 x float> %0
+}
+
+; CHECK-NOT: mfspr
+; CHECK-NOT: mtspr