[llvm] a0da66b - [SystemZ] Support builtin_frame_address with packed stack without backchain.

[Jonas Paulsson via llvm-commits]

Author: Jonas Paulsson
Date: 2021-05-06T12:50:49+02:00
New Revision: a0da66bc1330f9808ed9814aaa9c3c3d3244852d

URL: https://github.com/llvm/llvm-project/commit/a0da66bc1330f9808ed9814aaa9c3c3d3244852d
DIFF: https://github.com/llvm/llvm-project/commit/a0da66bc1330f9808ed9814aaa9c3c3d3244852d.diff

LOG: [SystemZ] Support builtin_frame_address with packed stack without backchain.

In order to use __builtin_frame_address(0) with packed stack and no
backchain, the address of where the backchain would have been written is
returned (like GCC).

This address may either contain a saved register or be unused.

Review: Ulrich Weigand

Differential Revision: https://reviews.llvm.org/D101897

Added: 
    

Modified: 
    llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
    llvm/test/CodeGen/SystemZ/frameaddr-02.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index 5e3af53dc9188..59c747d060c1c 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -3278,12 +3278,10 @@ SDValue SystemZTargetLowering::lowerFRAMEADDR(SDValue Op,
   unsigned Depth = cast<ConstantSDNode>(Op.getOperand(0))->getZExtValue();
   EVT PtrVT = getPointerTy(DAG.getDataLayout());
 
-  // Return null if the back chain is not present.
-  bool HasBackChain = MF.getFunction().hasFnAttribute("backchain");
-  if (TFL->usePackedStack(MF) && !HasBackChain)
-    return DAG.getConstant(0, DL, PtrVT);
-
-  // By definition, the frame address is the address of the back chain.
+  // By definition, the frame address is the address of the back chain.  (In
+  // the case of packed stack without backchain, return the address where the
+  // backchain would have been stored. This will either be an unused space or
+  // contain a saved register).
   int BackChainIdx = TFL->getOrCreateFramePointerSaveIndex(MF);
   SDValue BackChain = DAG.getFrameIndex(BackChainIdx, PtrVT);
 

diff  --git a/llvm/test/CodeGen/SystemZ/frameaddr-02.ll b/llvm/test/CodeGen/SystemZ/frameaddr-02.ll
index f1b62f6928a83..4d87f433958dd 100644
--- a/llvm/test/CodeGen/SystemZ/frameaddr-02.ll
+++ b/llvm/test/CodeGen/SystemZ/frameaddr-02.ll
@@ -33,22 +33,41 @@ attributes #1 = { nounwind "packed-stack" }
 define i8* @fp1() #1 {
 entry:
 ; CHECK-LABEL: fp1:
-; CHECK:      lghi %r2, 0
+; CHECK:      la   %r2, 152(%r15)
 ; CHECK-NEXT: br   %r14
   %0 = tail call i8* @llvm.frameaddress(i32 0)
   ret i8* %0
 }
 
+; No saved registers: returning address of unused slot where backcahin would
+; have been located.
 define i8* @fp1f() #1 {
 entry:
 ; CHECK-LABEL: fp1f:
-; CHECK:      aghi	%r15, -8
-; CHECK-NEXT: lghi	%r2, 0
-; CHECK-NEXT: aghi	%r15, 8
+; CHECK:      aghi	%r15, -16
+; CHECK-NEXT: la	%r2, 168(%r15)
+; CHECK-NEXT: aghi	%r15, 16
 ; CHECK-NEXT: br	%r14
   %0 = alloca i64, align 8
   %1 = tail call i8* @llvm.frameaddress(i32 0)
   ret i8* %1
 }
 
+; Saved registers: returning address for first saved GPR.
+declare void @foo(i8* %Arg)
+define i8* @fp2() #1 {
+entry:
+; CHECK-LABEL: fp2:
+; CHECK:      stmg      %r14, %r15, 144(%r15)
+; CHECK-NEXT: aghi	%r15, -16
+; CHECK-NEXT: la	%r2, 168(%r15)
+; CHECK-NEXT: brasl     %r14, foo at PLT
+; CHECK-NEXT: la	%r2, 168(%r15)
+; CHECK-NEXT: lmg       %r14, %r15, 160(%r15)
+; CHECK-NEXT: br	%r14
+  %0 = tail call i8* @llvm.frameaddress(i32 0)
+  call void @foo(i8* %0);
+  ret i8* %0
+}
+
 declare i8* @llvm.frameaddress(i32) nounwind readnone