Fix AArch64 prologue for empty frame with dynamic allocas.

Fixes PR23804: assertion failure in emitPrologue in the case of a
function with an empty frame and a dynamic alloca that needs stack
realignment. This is a typical case for AddressSanitizer.

llvm-svn: 241943

1 files changed, 4 insertions, 8 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index 3ba7e70a102..2e552cd300b 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -349,13 +349,12 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
   // Allocate space for the rest of the frame.
 
   const unsigned Alignment = MFI->getMaxAlignment();
-  const bool NeedsRealignment = (Alignment > 16);
+  const bool NeedsRealignment = RegInfo->needsStackRealignment(MF);
   unsigned scratchSPReg = AArch64::SP;
-  if (NeedsRealignment) {
-    // Use the first callee-saved register as a scratch register
-    assert(MF.getRegInfo().isPhysRegUsed(AArch64::X9) &&
-           "No scratch register to align SP!");
+  if (NumBytes && NeedsRealignment) {
+    // Use the first callee-saved register as a scratch register.
     scratchSPReg = AArch64::X9;
+    MF.getRegInfo().setPhysRegUsed(scratchSPReg);
   }
 
   // If we're a leaf function, try using the red zone.
@@ -366,9 +365,6 @@ void AArch64FrameLowering::emitPrologue(MachineFunction &MF,
     emitFrameOffset(MBB, MBBI, DL, scratchSPReg, AArch64::SP, -NumBytes, TII,
                     MachineInstr::FrameSetup);
 
-  assert(!(NeedsRealignment && NumBytes==0) &&
-         "NumBytes should never be 0 when realignment is needed");
-
   if (NumBytes && NeedsRealignment) {
     const unsigned NrBitsToZero = countTrailingZeros(Alignment);
     assert(NrBitsToZero > 1);