[llvm] [WebAssembly] Select BUILD_VECTOR with large unsigned lane values (PR #85880)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-webassembly

Author: Thomas Lively (tlively)

<details>
<summary>Changes</summary>

Previously we expected lane constants to be in the range of signed values for each lane size, but the included test case produced large unsigned values that fall outside that range. Allow instruction selection to proceed in this case rather than failing.

Fixes #<!-- -->63817.

---
Full diff: https://github.com/llvm/llvm-project/pull/85880.diff


2 Files Affected:

- (modified) llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td (+4-2) 
- (added) llvm/test/CodeGen/WebAssembly/pr63817.ll (+15) 


``````````diff
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
index 8cd41d7017a023..35f7d49be7a965 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrSIMD.td
@@ -46,10 +46,12 @@ defm "" : ARGUMENT<V128, v2i64>;
 defm "" : ARGUMENT<V128, v4f32>;
 defm "" : ARGUMENT<V128, v2f64>;
 
-// Constrained immediate argument types
+// Constrained immediate argument types. Allow any value from the minimum signed
+// value to the maximum unsigned value for the lane size.
 foreach SIZE = [8, 16] in
 def ImmI#SIZE : ImmLeaf<i32,
-  "return -(1 << ("#SIZE#" - 1)) <= Imm && Imm < (1 << ("#SIZE#" - 1));"
+  // -2^(n-1) <= Imm <= 2^n-1, avoiding UB when n == 64.
+  "return -(1 << ("#SIZE#" - 1)) <= Imm && Imm <= int64_t(uint64_t(1 << ("#SIZE#" - 1) << 1) - 1);"
 >;
 foreach SIZE = [2, 4, 8, 16, 32] in
 def LaneIdx#SIZE : ImmLeaf<i32, "return 0 <= Imm && Imm < "#SIZE#";">;
diff --git a/llvm/test/CodeGen/WebAssembly/pr63817.ll b/llvm/test/CodeGen/WebAssembly/pr63817.ll
new file mode 100644
index 00000000000000..252768d43f1888
--- /dev/null
+++ b/llvm/test/CodeGen/WebAssembly/pr63817.ll
@@ -0,0 +1,15 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=wasm32 -mattr=+simd128 | FileCheck %s
+
+;; Regression test for a bug in which BUILD_VECTOR nodes with large unsigned
+;; lane constants were not properly selected.
+define <4 x i8> @test(<4 x i8> %0) {
+; CHECK-LABEL: test:
+; CHECK:         .functype test (v128) -> (v128)
+; CHECK-NEXT:  # %bb.0:
+; CHECK-NEXT:    v128.const 255, 17, 255, 255, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+; CHECK-NEXT:    # fallthrough-return
+  %V1 = or <4 x i8> <i8 255, i8 255, i8 255, i8 255>, %0
+  %V2 = insertelement <4 x i8> %V1, i8 17, i32 1
+  ret <4 x i8> %V2
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/85880