[PowerPC] Clang Option for enabling absolute jumptables with command line

[kamaub]

Summary

This option allows the user to specify the use of absolute jumptables instead
of relative jumptables when they are running clang with the option:
-mllvm -ppc-use-absolute-jumptables

[NeHuang]

Overall looks good to me. Some minor changes needed.

llvm/test/CodeGen/PowerPC/absol-jump-table-enabled.ll

2

Please add a brief note at the top stating what you are testing here.

19

nit: alignment of blr

21

nit: alignment of jumpTableTest (one less space)

27

nit: alignment of blr

[amyk]

I have the same nits as @NeHuang, but this overall also looks good to me.

[kamaub]

Minor formatting changes to the test case.

[kamaub]

This comment was removed by kamaub.

[kamaub]

Thank you for your comments, I have addressed them.

[amyk]

llvm/test/CodeGen/PowerPC/absol-jump-table-enabled.ll

4

; NOTE: table works correctly.

[nemanjai]

LGTM (with Amy's comment addressed).

[kamaub]

• Minor spelling correction to test case comment

[kamaub]

Thank you, comment addressed.

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

 cl::desc("disable sibling call optimization on ppc"), cl::Hidden);
 
 static cl::opt<bool> DisableInnermostLoopAlign32("disable-ppc-innermost-loop-align32",
 cl::desc("don't always align innermost loop to 32 bytes on ppc"), cl::Hidden);
 
 static cl::opt<bool> EnableQuadPrecision("enable-ppc-quad-precision",
 cl::desc("enable quad precision float support on ppc"), cl::Hidden);
 
+static cl::opt<bool> UseAbsoluteJumpTables("ppc-use-absolute-jumptables",
+cl::desc("use absolute jump tables on ppc"), cl::Hidden);
+
 STATISTIC(NumTailCalls, "Number of tail calls");
 STATISTIC(NumSiblingCalls, "Number of sibling calls");
 
 static bool isNByteElemShuffleMask(ShuffleVectorSDNode *, unsigned, int);
 
 static SDValue widenVec(SelectionDAG &DAG, SDValue Vec, const SDLoc &dl);
 
 // FIXME: Remove this once the bug has been fixed!

 unsigned PPCTargetLowering::getJumpTableEncoding() const {
   if (isJumpTableRelative())
     return MachineJumpTableInfo::EK_LabelDifference32;
 
   return TargetLowering::getJumpTableEncoding();
 }
 
 bool PPCTargetLowering::isJumpTableRelative() const {
+  if (UseAbsoluteJumpTables)
+    return false;
   if (Subtarget.isPPC64())
     return true;
   return TargetLowering::isJumpTableRelative();
 }
 
 SDValue PPCTargetLowering::getPICJumpTableRelocBase(SDValue Table,
                                                     SelectionDAG &DAG) const {
   if (!Subtarget.isPPC64())

llvm/test/CodeGen/PowerPC/absol-jump-table-enabled.ll

+; NOTE: This test case generates a jump table on PowerPC big and little endian
+; NOTE: then verifies that the command line option to enable absolute jump
+; NOTE: table works correctly.
+; RUN:  llc -mtriple=powerpc64le-unknown-linux-gnu -o - \
+; RUN:      -ppc-use-absolute-jumptables -ppc-asm-full-reg-names \
+; RUN:      -verify-machineinstrs %s | FileCheck %s -check-prefix=CHECK-LE
+; RUN:  llc -mtriple=powerpc64-unknown-linux-gnu -o - \
+; RUN:      -ppc-use-absolute-jumptables -ppc-asm-full-reg-names \
+; RUN:      -verify-machineinstrs %s | FileCheck %s -check-prefix=CHECK-BE
+
+%struct.node = type { i8, %struct.node* }
+
+; Function Attrs: norecurse nounwind readonly
+define zeroext i32 @jumpTableTest(%struct.node* readonly %list) {
+; CHECK-LE-LABEL: jumpTableTest:
+; CHECK-LE:       # %bb.0: # %entry
+; CHECK-LE:       rldic r[[REG:[0-9]+]], r[[REG]], 3, 29
+; CHECK-LE:       ldx r[[REG]], r[[REG]], r[[REG1:[0-9]+]]
+; CHECK-LE:       mtctr r[[REG]]
+; CHECK-LE:       bctr
+; CHECK-LE:       blr
+;
+; CHECK-BE-LABEL: jumpTableTest:
+; CHECK-BE:       # %bb.0: # %entry
+; CHECK-BE:       rldic r[[REG:[0-9]+]], r[[REG]], 2, 30
+; CHECK-BE:       lwax r[[REG]], r[[REG]], r[[REG1:[0-9]+]]
+; CHECK-BE:       mtctr r[[REG]]
+; CHECK-BE:       bctr
+; CHECK-BE:       blr
+entry:
+  %cmp36 = icmp eq %struct.node* %list, null
+  br i1 %cmp36, label %while.end, label %while.body
+
+while.body:                                       ; preds = %entry, %sw.epilog
+  %result.038 = phi i32 [ %result.1, %sw.epilog ], [ 0, %entry ]
+  %current.037 = phi %struct.node* [ %spec.store.select, %sw.epilog ], [ %list, %entry ]
+  %next1 = getelementptr inbounds %struct.node, %struct.node* %current.037, i64 0, i32 1
+  %0 = load %struct.node*, %struct.node** %next1, align 8
+  %cmp2 = icmp eq %struct.node* %0, %current.037
+  %spec.store.select = select i1 %cmp2, %struct.node* null, %struct.node* %0
+  %type = getelementptr inbounds %struct.node, %struct.node* %current.037, i64 0, i32 0
+  %1 = load i8, i8* %type, align 8
+  switch i8 %1, label %sw.epilog [
+    i8 1, label %sw.bb
+    i8 2, label %sw.bb3
+    i8 3, label %sw.bb5
+    i8 4, label %sw.bb7
+    i8 5, label %sw.bb9
+    i8 6, label %sw.bb11
+    i8 7, label %sw.bb13
+    i8 8, label %sw.bb15
+    i8 9, label %sw.bb17
+  ]
+
+sw.bb:                                            ; preds = %while.body
+  %add = add nsw i32 %result.038, 13
+  br label %sw.epilog
+
+sw.bb3:                                           ; preds = %while.body
+  %add4 = add nsw i32 %result.038, 5
+  br label %sw.epilog
+
+sw.bb5:                                           ; preds = %while.body
+  %add6 = add nsw i32 %result.038, 2
+  br label %sw.epilog
+
+sw.bb7:                                           ; preds = %while.body
+  %add8 = add nsw i32 %result.038, 7
+  br label %sw.epilog
+
+sw.bb9:                                           ; preds = %while.body
+  %add10 = add nsw i32 %result.038, 11
+  br label %sw.epilog
+
+sw.bb11:                                          ; preds = %while.body
+  %add12 = add nsw i32 %result.038, 17
+  br label %sw.epilog
+
+sw.bb13:                                          ; preds = %while.body
+  %add14 = add nsw i32 %result.038, 16
+  br label %sw.epilog
+
+sw.bb15:                                          ; preds = %while.body
+  %add16 = add nsw i32 %result.038, 81
+  br label %sw.epilog
+
+sw.bb17:                                          ; preds = %while.body
+  %add18 = add nsw i32 %result.038, 72
+  br label %sw.epilog
+
+sw.epilog:                                        ; preds = %while.body, %sw.bb17, %sw.bb15, %sw.bb13, %sw.bb11, %sw.bb9, %sw.bb7, %sw.bb5, %sw.bb3, %sw.bb
+  %result.1 = phi i32 [ %result.038, %while.body ], [ %add18, %sw.bb17 ], [ %add16, %sw.bb15 ], [ %add14, %sw.bb13 ], [ %add12, %sw.bb11 ], [ %add10, %sw.bb9 ], [ %add8, %sw.bb7 ], [ %add6, %sw.bb5 ], [ %add4, %sw.bb3 ], [ %add, %sw.bb ]
+  %cmp = icmp eq %struct.node* %spec.store.select, null
+  br i1 %cmp, label %while.end, label %while.body
+
+while.end:                                        ; preds = %sw.epilog, %entry
+  %result.0.lcssa = phi i32 [ 0, %entry ], [ %result.1, %sw.epilog ]
+  ret i32 %result.0.lcssa
+}
+