llvm: Use correct type for splat mask

maurer · maurer · commit 3c83d3adc91b · 2026-05-05T19:14:39.000Z
After llvm/llvm-project#195486 , LLVM has explicit handling for null pointers in simd operations instead of using special handling based on zeroes. This causes LLVM with asserts enabled to detect an improperly typed mask passed to splat (if the output vector does not have i32 elements), and can cause SIGSEGV in more complex cases with asserts disabled.
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -2086,7 +2086,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
     }
 
     if name == sym::simd_splat {
-        let (_out_len, out_ty) = require_simd!(ret_ty, SimdReturn);
+        let (out_len, out_ty) = require_simd!(ret_ty, SimdReturn);
 
         require!(
             args[0].layout.ty == out_ty,
@@ -2105,7 +2105,8 @@ fn generic_simd_intrinsic<'ll, 'tcx>(
 
         // `shufflevector <N x elem> v0, <N x elem> poison, <N x i32> zeroinitializer`
         // The masks is all zeros, so this splats lane 0 (which has our element in it).
-        let splat = bx.shuffle_vector(v0, poison_vec, bx.const_null(llret_ty));
+        let mask_ty = bx.type_vector(bx.type_i32(), out_len);
+        let splat = bx.shuffle_vector(v0, poison_vec, bx.const_null(mask_ty));
 
         return Ok(splat);
     }

Original file line number	Diff line number	Diff line change
`@@ -2086,7 +2086,7 @@ fn generic_simd_intrinsic<'ll, 'tcx>(`
`2086`	`2086`	`}`
`2087`	`2087`
`2088`	`2088`	`if name == sym::simd_splat {`
`2089`		`- let (_out_len, out_ty) = require_simd!(ret_ty, SimdReturn);`
	`2089`	`+ let (out_len, out_ty) = require_simd!(ret_ty, SimdReturn);`
`2090`	`2090`
`2091`	`2091`	`require!(`
`2092`	`2092`	`args[0].layout.ty == out_ty,`
`@@ -2105,7 +2105,8 @@ fn generic_simd_intrinsic<'ll, 'tcx>(`
`2105`	`2105`
`2106`	`2106`	// `shufflevector <N x elem> v0, <N x elem> poison, <N x i32> zeroinitializer`
`2107`	`2107`	`// The masks is all zeros, so this splats lane 0 (which has our element in it).`
`2108`		`- let splat = bx.shuffle_vector(v0, poison_vec, bx.const_null(llret_ty));`
	`2108`	`+ let mask_ty = bx.type_vector(bx.type_i32(), out_len);`
	`2109`	`+ let splat = bx.shuffle_vector(v0, poison_vec, bx.const_null(mask_ty));`
`2109`	`2110`
`2110`	`2111`	`return Ok(splat);`
`2111`	`2112`	`}`