[clang] [Driver] Pass correct alignment for -falign-functions with no argument (PR #101257)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Paul T Robinson (pogo59)

<details>
<summary>Changes</summary>

-falign-functions with no argument is supposed to be equivalent to -falign-functions=16, according to the documentation. Make it so.

---
Full diff: https://github.com/llvm/llvm-project/pull/101257.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/CommonArgs.cpp (+1-1) 
- (modified) clang/test/Driver/function-alignment.c (+2-1) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 1e37d9d348818..bc74f9afcf868 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1982,7 +1982,7 @@ unsigned tools::ParseFunctionAlignment(const ToolChain &TC,
     return 0;
 
   if (A->getOption().matches(options::OPT_falign_functions))
-    return 0;
+    return 4; // log2(16)
 
   unsigned Value = 0;
   if (StringRef(A->getValue()).getAsInteger(10, Value) || Value > 65536)
diff --git a/clang/test/Driver/function-alignment.c b/clang/test/Driver/function-alignment.c
index ed4cc80f7ed4f..b0eb7cfdad8cc 100644
--- a/clang/test/Driver/function-alignment.c
+++ b/clang/test/Driver/function-alignment.c
@@ -1,5 +1,5 @@
 // RUN: %clang -### %s 2>&1 | FileCheck %s -check-prefix CHECK-0
-// RUN: %clang -### -falign-functions %s 2>&1 | FileCheck %s -check-prefix CHECK-1
+// RUN: %clang -### -falign-functions %s 2>&1 | FileCheck %s -check-prefix CHECK-16
 // RUN: %clang -### -falign-functions=1 %s 2>&1 | FileCheck %s -check-prefix CHECK-1
 // RUN: %clang -### -falign-functions=2 %s 2>&1 | FileCheck %s -check-prefix CHECK-2
 // RUN: %clang -### -falign-functions=3 %s 2>&1 | FileCheck %s -check-prefix CHECK-3
@@ -8,6 +8,7 @@
 // RUN: not %clang -### -falign-functions=a %s 2>&1 | FileCheck %s -check-prefix CHECK-ERR-A
 
 // CHECK-0-NOT: "-function-alignment"
+// CHECK-16: "-function-alignment" "4"
 // CHECK-1-NOT: "-function-alignment"
 // CHECK-2: "-function-alignment" "1"
 // CHECK-3: "-function-alignment" "2"

``````````

</details>


https://github.com/llvm/llvm-project/pull/101257