[PowerPC] Option for enabling absolute jumptables with command line

This option allows the user to specify the use of absolute jumptables instead
of relative which is the default on most PPC subtargets.

Patch by Kamauu Bridgeman

Differential revision: https://reviews.llvm.org/D69108

2 files changed, 105 insertions, 0 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index 87ba74cf860..a2ffe9e3540 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -119,6 +119,9 @@ 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");
 
@@ -2744,6 +2747,8 @@ unsigned PPCTargetLowering::getJumpTableEncoding() const {
 }
 
 bool PPCTargetLowering::isJumpTableRelative() const {
+  if (UseAbsoluteJumpTables)
+    return false;
   if (Subtarget.isPPC64())
     return true;
   return TargetLowering::isJumpTableRelative();
diff --git a/llvm/test/CodeGen/PowerPC/absol-jump-table-enabled.ll b/llvm/test/CodeGen/PowerPC/absol-jump-table-enabled.ll
new file mode 100644
index 00000000000..4a9492d8e10
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/absol-jump-table-enabled.ll
@@ -0,0 +1,100 @@
+; 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
+}
+