[XRay] xray_fn_idx: fix alignment directive

Use `emitValueToAlignment` as the section does not contain code.
`emitCodeAlignment` would lead to ALIGN relocations on RISC-V and
LoongArch with linker relaxation.

In addition, change the alignment to wordsize, sufficient for the
runtime requirement (`XRayFunctionSledIndex`).

Related to #147322

Author: MaskRay

llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -4628,12 +4628,10 @@ void AsmPrinter::emitXRayTable() {
 
   // We then emit a single entry in the index per function. We use the symbols
   // that bound the instrumentation map as the range for a specific function.
-  // Each entry here will be 2 * word size aligned, as we're writing down two
-  // pointers. This should work for both 32-bit and 64-bit platforms.
+  // Each entry contains 2 words and needs to be word-aligned.
   if (FnSledIndex) {
     OutStreamer->switchSection(FnSledIndex);
-    OutStreamer->emitCodeAlignment(Align(2 * WordSizeBytes),
-                                   &getSubtargetInfo());
+    OutStreamer->emitValueToAlignment(Align(WordSizeBytes));
     // For Mach-O, use an "l" symbol as the atom of this subsection. The label
     // difference uses a SUBTRACTOR external relocation which references the
     // symbol.

llvm/test/CodeGen/PowerPC/xray-attribute-instrumentation.ll

@@ -41,7 +41,7 @@ define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always"
 ; CHECK-NEXT:         .space  13
 ; CHECK-NEXT: .Lxray_sleds_end0:
 ; CHECK-LABEL: xray_fn_idx,"ao",@progbits,foo{{$}}
-; CHECK:              .p2align        4
+; CHECK:              .p2align        3, 0x0
 ; CHECK-NEXT: [[IDX:.Lxray_fn_idx[0-9]+]]:
 ; CHECK-NEXT:         .quad .Lxray_sleds_start0-[[IDX]]
 ; CHECK-NEXT:         .quad 2

llvm/test/CodeGen/SystemZ/xray.ll

@@ -38,7 +38,7 @@ define signext i32 @foo() "function-instrument"="xray-always" {
 ; CHECK: 	.space	13
 ; CHECK: .Lxray_sleds_end0:
 ; CHECK: 	.section	xray_fn_idx,"ao",@progbits,foo
-; CHECK: 	.p2align	4
+; CHECK: 	.p2align	3, 0
 ; CHECK: .Lxray_fn_idx0:
 ; CHECK: 	.quad	.Lxray_sleds_start0-.Lxray_fn_idx0
 ; CHECK: 	.quad	2

llvm/test/CodeGen/X86/xray-attribute-instrumentation.ll

@@ -20,7 +20,8 @@ define i32 @foo() nounwind noinline uwtable "function-instrument"="xray-always"
 ; CHECK-LINUX:         .quad .Lxray_sled_1
 ; CHECK-LINUX-LABEL: .Lxray_sleds_end0:
 ; CHECK-LINUX-LABEL: .section xray_fn_idx,"ao",@progbits,foo{{$}}
-; CHECK-LINUX:       [[IDX:\.Lxray_fn_idx[0-9]+]]:
+; CHECK-LINUX-NEXT:    .p2align 3, 0x0
+; CHECK-LINUX-NEXT:  [[IDX:\.Lxray_fn_idx[0-9]+]]:
 ; CHECK-LINUX-NEXT:    .quad .Lxray_sleds_start0-[[IDX]]
 ; CHECK-LINUX-NEXT:    .quad 2