[PowerPC] Fix label address calculation for ppc32

[spetrovic]

Summary

This patch fixes calculating address of label on ppc32 (for -fPIC), I was using gcc as reference. You can try to run this example with and without the patch and see the difference:

unsigned int foo(void) {

return 0;

}

int main() {
L: attribute ((unused));

static const unsigned int arr[] =
{
  (unsigned int) &&x  - (unsigned int)&&L ,
  (unsigned int) &&y  - (unsigned int)&&L
};

unsigned int ret = foo();
void* g = (void *) ((unsigned int)&&L + arr[ret]);
goto *g;

x:

return 15;

y:

return 25;

}

[spetrovic]

ping

[hfinkel]

lib/Target/PowerPC/PPCISelLowering.cpp

2575–2577

I don't think that we should be calling setUsesTOCBasePtr outside of 64-bit code.

[spetrovic]

ping

[hfinkel]

LGTM

lib/Target/PowerPC/PPCISelLowering.cpp

 SDValue PPCTargetLowering::LowerBlockAddress(SDValue Op,
                                              SelectionDAG &DAG) const {
   EVT PtrVT = Op.getValueType();
   BlockAddressSDNode *BASDN = cast<BlockAddressSDNode>(Op);
   const BlockAddress *BA = BASDN->getBlockAddress();
 
   // 64-bit SVR4 ABI code is always position-independent.
   // The actual BlockAddress is stored in the TOC.
-  if (Subtarget.isSVR4ABI() && Subtarget.isPPC64()) {
+  if (Subtarget.isSVR4ABI() && isPositionIndependent()) {
+    if (Subtarget.isPPC64())
       setUsesTOCBasePtr(DAG);
     SDValue GA = DAG.getTargetBlockAddress(BA, PtrVT, BASDN->getOffset());
-    return getTOCEntry(DAG, SDLoc(BASDN), true, GA);
+    return getTOCEntry(DAG, SDLoc(BASDN), Subtarget.isPPC64(), GA);
   }
 
   unsigned MOHiFlag, MOLoFlag;
   bool IsPIC = isPositionIndependent();
   getLabelAccessInfo(IsPIC, Subtarget, MOHiFlag, MOLoFlag);
   SDValue TgtBAHi = DAG.getTargetBlockAddress(BA, PtrVT, 0, MOHiFlag);
   SDValue TgtBALo = DAG.getTargetBlockAddress(BA, PtrVT, 0, MOLoFlag);
   return LowerLabelRef(TgtBAHi, TgtBALo, IsPIC, DAG);

test/CodeGen/PowerPC/ppc-label.ll

+; RUN: llc < %s -mtriple=powerpc-unknown-linux-gnu -relocation-model=pic | FileCheck %s
+
+; unsigned int foo(void) {
+;   return 0;
+; }
+;
+; int main() {
+; L: __attribute__ ((unused));
+;   static const unsigned int arr[] =
+;   {
+;     (unsigned int) &&x  - (unsigned int)&&L ,
+;     (unsigned int) &&y  - (unsigned int)&&L
+;   };
+;
+;   unsigned int ret = foo();
+;   void* g = (void *) ((unsigned int)&&L + arr[ret]);
+;   goto *g;
+;
+; x:
+;   return 15;
+; y:
+;   return 25;
+; }
+
+define i32 @foo() local_unnamed_addr {
+entry:
+  ret i32 0
+}
+
+define i32 @main() {
+entry:
+  br label %L
+
+L:                                                ; preds = %L, %entry
+  indirectbr i8* inttoptr (i32 add (i32 ptrtoint (i8* blockaddress(@main, %L) to i32), i32 sub (i32 ptrtoint (i8* blockaddress(@main, %return) to i32), i32 ptrtoint (i8* blockaddress(@main, %L) to i32))) to i8*), [label %return, label %L]
+
+return:                                           ; preds = %L
+  ret i32 15
+}
+
+
+; CHECK:     lwz 3, .LC0-.LTOC(30)
+; CHECK-NOT: li 3, .Ltmp1-.L1$pb@l
+; CHECK-NOT: addis 4, 30, .Ltmp1-.L1$pb@ha
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