[llvm] [BPF] Define set of BPF libcalls (PR #169537)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Lucas Ste (LucasSte)

<details>
<summary>Changes</summary>

**Problem**

Following the comment in https://github.com/llvm/llvm-project/pull/168442#pullrequestreview-3501502448, we can define which libcalls are available in BPF, so that i128 arithmetics and i64 arithmetics with overflow detection can correctly work in BPF.


**Solution**

Exclude from the default set all i128 related arithmetic operations.

---
Full diff: https://github.com/llvm/llvm-project/pull/169537.diff


3 Files Affected:

- (modified) llvm/include/llvm/IR/RuntimeLibcalls.td (+17) 
- (removed) llvm/test/CodeGen/BPF/builtin_calls.ll (-39) 
- (added) llvm/test/CodeGen/BPF/i128_math.ll (+23) 


``````````diff
diff --git a/llvm/include/llvm/IR/RuntimeLibcalls.td b/llvm/include/llvm/IR/RuntimeLibcalls.td
index 11e6127e0741d..d0e2eafdd0538 100644
--- a/llvm/include/llvm/IR/RuntimeLibcalls.td
+++ b/llvm/include/llvm/IR/RuntimeLibcalls.td
@@ -2808,6 +2808,23 @@ def WasmSystemLibrary
            emscripten_return_address,
            __stack_chk_fail, __stack_chk_guard)>;
 
+//===----------------------------------------------------------------------===//
+// BPF Runtime Libcalls
+//===----------------------------------------------------------------------===//
+
+def isBPF : RuntimeLibcallPredicate<"TT.isBPF()">;
+
+def BPFSystemLibrary
+    : SystemRuntimeLibrary<isBPF,
+      (add (sub DefaultRuntimeLibcallImpls,
+      // i128 operations should be lowered by LLVM for BPF
+       __divti3,
+       __udivti3,
+       __modti3,
+       __umodti3,
+       __clzti2
+    ))>;
+
 //===----------------------------------------------------------------------===//
 // Legacy Default Runtime Libcalls
 //===----------------------------------------------------------------------===//
diff --git a/llvm/test/CodeGen/BPF/builtin_calls.ll b/llvm/test/CodeGen/BPF/builtin_calls.ll
deleted file mode 100644
index 18199eba7222a..0000000000000
--- a/llvm/test/CodeGen/BPF/builtin_calls.ll
+++ /dev/null
@@ -1,39 +0,0 @@
-; RUN: llc -march=bpfel -mattr=+allow-builtin-calls < %s | FileCheck %s
-;
-; C code for this test case:
-;
-; long func(long a, long b) {
-;     long x;
-;     return __builtin_mul_overflow(a, b, &x);
-; }
-
-
-declare { i64, i1 } @llvm.smul.with.overflow.i64(i64, i64)
-
-define noundef range(i64 0, 2) i64 @func(i64 noundef %a, i64 noundef %b) local_unnamed_addr {
-entry:
-  %0 = tail call { i64, i1 } @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
-  %1 = extractvalue { i64, i1 } %0, 1
-  %conv = zext i1 %1 to i64
-  ret i64 %conv
-}
-
-; CHECK-LABEL: func
-; CHECK: r4 = r2
-; CHECK: r2 = r1
-; CHECK: r3 = r2
-; CHECK: r3 s>>= 63
-; CHECK: r5 = r4
-; CHECK: r5 s>>= 63
-; CHECK: r1 = r10
-; CHECK: r1 += -16
-; CHECK: call __multi3
-; CHECK: r1 = *(u64 *)(r10 - 16)
-; CHECK: r1 s>>= 63
-; CHECK: w0 = 1
-; CHECK: r2 = *(u64 *)(r10 - 8)
-; CHECK: if r2 != r1 goto LBB0_2
-; CHECK:  # %bb.1:                                # %entry
-; CHECK: w0 = 0
-; CHECK:  LBB0_2:                                 # %entry
-; CHECK: exit
\ No newline at end of file
diff --git a/llvm/test/CodeGen/BPF/i128_math.ll b/llvm/test/CodeGen/BPF/i128_math.ll
new file mode 100644
index 0000000000000..6fbbdfe4662c3
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/i128_math.ll
@@ -0,0 +1,23 @@
+; RUN: llc -march=bpfel < %s | FileCheck %s
+;
+; C code for this test case:
+;
+; long func(long a, long b) {
+;     long x;
+;     return __builtin_mul_overflow(a, b, &x);
+; }
+
+
+declare { i64, i1 } @llvm.smul.with.overflow.i64(i64, i64)
+
+define noundef range(i64 0, 2) i64 @func(i64 noundef %a, i64 noundef %b) local_unnamed_addr {
+entry:
+  %0 = tail call { i64, i1 } @llvm.smul.with.overflow.i64(i64 %a, i64 %b)
+  %1 = extractvalue { i64, i1 } %0, 1
+  %conv = zext i1 %1 to i64
+  ret i64 %conv
+}
+
+; CHECK-LABEL: func
+; CHECK-NOT: call __multi3
+; CHECK: exit

``````````

</details>


https://github.com/llvm/llvm-project/pull/169537