[ARM] mlong-calls generate PIC code using GOT #39970

[jiangxuezhi]

supoort -mlong-calls -fPIC using GOT
try fixing issuse #39970 and maybe helpful for soving the problem encourted in #142982

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[llvmbot]

@llvm/pr-subscribers-backend-arm

Author: None (jiangxuezhi)

Changes

supoort -mlong-calls -fPIC using GOT
try fixing issuse #39970 and maybe helpful for soving the problem encourted in #142982

---

Full diff: https://github.com/llvm/llvm-project/pull/147313.diff

2 Files Affected:

• (modified) llvm/lib/Target/ARM/ARMISelLowering.cpp (+12-4)
• (added) llvm/test/CodeGen/ARM/long-calls.ll (+32)

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 2d73725291d11..b73a53cca84e3 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -2815,13 +2815,20 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
   auto PtrVt = getPointerTy(DAG.getDataLayout());
 
   if (Subtarget->genLongCalls()) {
-    assert((!isPositionIndependent() || Subtarget->isTargetWindows()) &&
-           "long-calls codegen is not position independent!");
     // Handle a global address or an external symbol. If it's not one of
     // those, the target's already in a register, so we don't need to do
     // anything extra.
     if (isa<GlobalAddressSDNode>(Callee)) {
-      if (Subtarget->genExecuteOnly()) {
+      if (isPositionIndependent() && !Subtarget->isTargetWindows() &&
+          !Subtarget->genExecuteOnly()) {
+        SDValue G = DAG.getTargetGlobalAddress(
+            GVal, dl, PtrVt, 0, GVal->isDSOLocal() ? 0 : ARMII::MO_GOT);
+        Callee = DAG.getNode(ARMISD::WrapperPIC, dl, PtrVt, G);
+        if (!GVal->isDSOLocal())
+          Callee =
+              DAG.getLoad(PtrVt, dl, DAG.getEntryNode(), Callee,
+                          MachinePointerInfo::getGOT(DAG.getMachineFunction()));
+      } else if (Subtarget->genExecuteOnly()) {
         if (Subtarget->useMovt())
           ++NumMovwMovt;
         Callee = DAG.getNode(ARMISD::Wrapper, dl, PtrVt,
@@ -2839,7 +2846,8 @@ ARMTargetLowering::LowerCall(TargetLowering::CallLoweringInfo &CLI,
             PtrVt, dl, DAG.getEntryNode(), Addr,
             MachinePointerInfo::getConstantPool(DAG.getMachineFunction()));
       }
-    } else if (ExternalSymbolSDNode *S=dyn_cast<ExternalSymbolSDNode>(Callee)) {
+    } else if (ExternalSymbolSDNode *S =
+                   dyn_cast<ExternalSymbolSDNode>(Callee)) {
       const char *Sym = S->getSymbol();
 
       if (Subtarget->genExecuteOnly()) {
diff --git a/llvm/test/CodeGen/ARM/long-calls.ll b/llvm/test/CodeGen/ARM/long-calls.ll
new file mode 100644
index 0000000000000..41763801fddd2
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/long-calls.ll
@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=armv7-unknown-linux-gnueabi -relocation-model pic -mattr=+long-calls -o - %s \
+; RUN:    | FileCheck %s
+
+@msg = private unnamed_addr constant [12 x i8] c"hello world\00", align 1
+
+declare i32 @puts(ptr)
+
+define void @test() {
+; CHECK-LABEL: test:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r11, lr}
+; CHECK-NEXT:    push {r11, lr}
+; CHECK-NEXT:    ldr r0, .LCPI0_0
+; CHECK-NEXT:    ldr r1, .LCPI0_1
+; CHECK-NEXT:  .LPC0_0:
+; CHECK-NEXT:    add r0, pc, r0
+; CHECK-NEXT:  .LPC0_1:
+; CHECK-NEXT:    ldr r1, [pc, r1]
+; CHECK-NEXT:    blx r1
+; CHECK-NEXT:    pop {r11, pc}
+; CHECK-NEXT:    .p2align 2
+; CHECK-NEXT:  @ %bb.1:
+; CHECK-NEXT:  .LCPI0_0:
+; CHECK-NEXT:    .long .Lmsg-(.LPC0_0+8)
+; CHECK-NEXT:  .LCPI0_1:
+; CHECK-NEXT:  .Ltmp0:
+; CHECK-NEXT:    .long puts(GOT_PREL)-(.LPC0_1+8-.Ltmp0)
+entry:
+  %call = call i32 @puts(ptr @msg)
+  ret void
+}

[jiangxuezhi]

e.g.
the command is clang -O2 -mlong-calls -fPIC

the code is:
#include <stdio.h>

int main()
{
printf("hello");
return 0;
}

the Relocation section is:
Offset Info Type Sym. Value Symbol's Name
00000020 00000503 R_ARM_REL32 00000000 .L.str
00000024 00000760 R_ARM_GOT_PREL 00000000 printf

Relocation section '.rel.ARM.exidx' at offset 0x1a8 contains 1 entry:
Offset Info Type Sym. Value Symbol's Name
00000000 0000022a R_ARM_PREL31 00000000 .text

[efriedma-quic]

Can this be integrated into llvm/test/CodeGen/ARM/subtarget-features-long-calls.ll?

[efriedma-quic]

Does the execute-only codepath work correctly with PIC?

[efriedma-quic]

Does the external-symbol codepath work correctly with PIC? (I think you can trigger this with llvm.memset or something like that.)