[Sparc] Account for bias in stack readjustment

Summary: This was broken long ago in D12208, which failed to account for
the fact that 64-bit SPARC uses a stack bias of 2047, and it is the
*unbiased* value which should be aligned, not the biased one. This was
seen to be an issue with Rust.

Patch by: jrtc27 (James Clarke)

Reviewers: jyknight, venkatra

Reviewed By: jyknight

Subscribers: jacob_hansen, JDevlieghere, fhahn, fedor.sergeev, llvm-commits

Differential Revision: https://reviews.llvm.org/D39425

llvm-svn: 323643

1 files changed, 24 insertions, 5 deletions

diff --git a/llvm/lib/Target/Sparc/SparcFrameLowering.cpp b/llvm/lib/Target/Sparc/SparcFrameLowering.cpp
index 9864aa37235..9f6c7d65592 100644
--- a/llvm/lib/Target/Sparc/SparcFrameLowering.cpp
+++ b/llvm/lib/Target/Sparc/SparcFrameLowering.cpp
@@ -88,10 +88,11 @@ void SparcFrameLowering::emitPrologue(MachineFunction &MF,
 
   assert(&MF.front() == &MBB && "Shrink-wrapping not yet supported");
   MachineFrameInfo &MFI = MF.getFrameInfo();
+  const SparcSubtarget &Subtarget = MF.getSubtarget<SparcSubtarget>();
   const SparcInstrInfo &TII =
-      *static_cast<const SparcInstrInfo *>(MF.getSubtarget().getInstrInfo());
+      *static_cast<const SparcInstrInfo *>(Subtarget.getInstrInfo());
   const SparcRegisterInfo &RegInfo =
-      *static_cast<const SparcRegisterInfo *>(MF.getSubtarget().getRegisterInfo());
+      *static_cast<const SparcRegisterInfo *>(Subtarget.getRegisterInfo());
   MachineBasicBlock::iterator MBBI = MBB.begin();
   // Debug location must be unknown since the first debug location is used
   // to determine the end of the prologue.
@@ -141,7 +142,7 @@ void SparcFrameLowering::emitPrologue(MachineFunction &MF,
 
   // Adds the SPARC subtarget-specific spill area to the stack
   // size. Also ensures target-required alignment.
-  NumBytes = MF.getSubtarget<SparcSubtarget>().getAdjustedFrameSize(NumBytes);
+  NumBytes = Subtarget.getAdjustedFrameSize(NumBytes);
 
   // Finally, ensure that the size is sufficiently aligned for the
   // data on the stack.
@@ -176,9 +177,27 @@ void SparcFrameLowering::emitPrologue(MachineFunction &MF,
       .addCFIIndex(CFIIndex);
 
   if (NeedsStackRealignment) {
-    // andn %o6, MaxAlign-1, %o6
+    int64_t Bias = Subtarget.getStackPointerBias();
+    unsigned regUnbiased;
+    if (Bias) {
+      // This clobbers G1 which we always know is available here.
+      regUnbiased = SP::G1;
+      // add %o6, BIAS, %g1
+      BuildMI(MBB, MBBI, dl, TII.get(SP::ADDri), regUnbiased)
+        .addReg(SP::O6).addImm(Bias);
+    } else
+      regUnbiased = SP::O6;
+
+    // andn %regUnbiased, MaxAlign-1, %regUnbiased
     int MaxAlign = MFI.getMaxAlignment();
-    BuildMI(MBB, MBBI, dl, TII.get(SP::ANDNri), SP::O6).addReg(SP::O6).addImm(MaxAlign - 1);
+    BuildMI(MBB, MBBI, dl, TII.get(SP::ANDNri), regUnbiased)
+      .addReg(regUnbiased).addImm(MaxAlign - 1);
+
+    if (Bias) {
+      // add %g1, -BIAS, %o6
+      BuildMI(MBB, MBBI, dl, TII.get(SP::ADDri), SP::O6)
+        .addReg(regUnbiased).addImm(-Bias);
+    }
   }
 }