[llvm] [BPF] Support Jump Table (PR #149715)

[via llvm-commits]

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@@ -0,0 +1,91 @@
+; Checks generated using command:
+;    llvm/utils/update_test_body.py llvm/test/CodeGen/BPF/jump_table_blockaddr.ll
+
+; RUN: rm -rf %t && split-file %s %t && cd %t
+; RUN: llc -march=bpf -mcpu=v4 < test.ll | FileCheck %s
+;
+; Source code:
+;    int bar(int a) {
+;       __label__ l1, l2;
+;       void * volatile tgt;
+;       int ret = 0;
+;       if (a)
+;         tgt = &&l1; // synthetic jump table generated here
+;       else
+;         tgt = &&l2; // another synthetic jump table
+;       goto *tgt;
+;   l1: ret += 1;
+;   l2: ret += 2;
+;       return ret;
+;     }
+;
+; Compilation Flags:
+;   clang --target=bpf -mcpu=v4 -O2 -emit-llvm -S test.c
+
+.ifdef GEN
+;--- test.ll
+define dso_local range(i32 2, 4) i32 @bar(i32 noundef %a) local_unnamed_addr{
+entry:
+  %tgt = alloca ptr, align 8
+  %tobool.not = icmp eq i32 %a, 0
+  %. = select i1 %tobool.not, ptr blockaddress(@bar, %l2), ptr blockaddress(@bar, %l1)
+  store volatile ptr %., ptr %tgt, align 8
+  %tgt.0.tgt.0.tgt.0.tgt.0. = load volatile ptr, ptr %tgt, align 8
+  indirectbr ptr %tgt.0.tgt.0.tgt.0.tgt.0., [label %l1, label %l2]
+
+l1:                                               ; preds = %entry
+  br label %l2
+
+l2:                                               ; preds = %l1, %entry
+  %ret.0 = phi i32 [ 3, %l1 ], [ 2, %entry ]
+  ret i32 %ret.0
+}
+
+;--- gen
+echo ""
+echo "; Generated checks follow"
+echo ";"
+llc -march=bpf -mcpu=v4 < test.ll \
+  | awk '/# -- End function/ {p=0} /@function/ {p=1} p {print "; CHECK" ": " $0}'
+
+.endif
+
+; Generated checks follow
+;
+; CHECK: 	.type	bar, at function
+; CHECK: bar:                                    # @bar
+; CHECK: .Lbar$local:
+; CHECK: 	.type	.Lbar$local, at function
+; CHECK: 	.cfi_startproc
+; CHECK: # %bb.0:                                # %entry
+; CHECK: 	r2 = BPF.JT.0.0 ll
+; CHECK: 	r2 = *(u64 *)(r2 + 0)
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yonghong-song wrote:

I think we are fine here. If anything changed, the CHECKs can be easily regenerated with `update_test_body.py` script. Specific register numbers are helpful to ensure asm code correctness.

https://github.com/llvm/llvm-project/pull/149715