[clang] 2dc6e98 - Revert "[Clang] Enable -fextend-lifetimes at -Og (#118026)"

[Stephen Tozer via cfe-commits]

Author: Stephen Tozer
Date: 2025-04-25T12:55:10+01:00
New Revision: 2dc6e98169baeb1f73036da0ea50fd828d8323d0

URL: https://github.com/llvm/llvm-project/commit/2dc6e98169baeb1f73036da0ea50fd828d8323d0
DIFF: https://github.com/llvm/llvm-project/commit/2dc6e98169baeb1f73036da0ea50fd828d8323d0.diff

LOG: Revert "[Clang] Enable -fextend-lifetimes at -Og (#118026)"

Reverted following several issues appearing related to fake uses, reported
on the github PR.

This reverts commit a9dff35ad251cd20376ab25b26d1e5394e18ff4c.

Added: 
    

Modified: 
    clang/docs/CommandGuide/clang.rst
    clang/docs/ReleaseNotes.rst
    clang/lib/Driver/ToolChains/Clang.cpp
    clang/test/Driver/extend-variable-liveness.c

Removed: 
    


################################################################################
diff  --git a/clang/docs/CommandGuide/clang.rst b/clang/docs/CommandGuide/clang.rst
index a1e738f1afec8..42aac7b25d93c 100644
--- a/clang/docs/CommandGuide/clang.rst
+++ b/clang/docs/CommandGuide/clang.rst
@@ -443,11 +443,8 @@ Code Generation Options
     :option:`-Oz` Like :option:`-Os` (and thus :option:`-O2`), but reduces code
     size further.
 
-    :option:`-Og` Similar to :option:`-O1`, but with slightly reduced
-    optimization and better variable visibility. The same optimizations are run
-    as at :option:`-O1`, but the ``-fextend-variable-liveness`` flag is
-    also set, which tries to prevent optimizations from reducing the liveness of
-    user variables, improving their availability when debugging.
+    :option:`-Og` Like :option:`-O1`. In future versions, this option might
+    disable 
diff erent optimizations in order to improve debuggability.
 
     :option:`-O` Equivalent to :option:`-O1`.
 

diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index d1f24fb23d44d..8140f6cc708c8 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -230,10 +230,6 @@ Modified Compiler Flags
 
 - The ``-mexecute-only`` and ``-mpure-code`` flags are now accepted for AArch64 targets. (#GH125688)
 
-- The ``-Og`` optimization flag now sets ``-fextend-variable-liveness``,
-  reducing performance slightly while reducing the number of optimized-out
-  variables.
-
 Removed Compiler Flags
 -------------------------
 

diff  --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index f98cd389509cd..762f8af886920 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -7683,13 +7683,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (Args.hasArg(options::OPT_fretain_comments_from_system_headers))
     CmdArgs.push_back("-fretain-comments-from-system-headers");
 
-  if (Arg *A = Args.getLastArg(options::OPT_fextend_variable_liveness_EQ)) {
-    A->render(Args, CmdArgs);
-  } else if (Arg *A = Args.getLastArg(options::OPT_O_Group);
-             A && A->containsValue("g")) {
-    // Set -fextend-variable-liveness=all by default at -Og.
-    CmdArgs.push_back("-fextend-variable-liveness=all");
-  }
+  Args.AddLastArg(CmdArgs, options::OPT_fextend_variable_liveness_EQ);
 
   // Forward -fcomment-block-commands to -cc1.
   Args.AddAllArgs(CmdArgs, options::OPT_fcomment_block_commands);

diff  --git a/clang/test/Driver/extend-variable-liveness.c b/clang/test/Driver/extend-variable-liveness.c
index 99a5409ceccea..bbfb2ece6f297 100644
--- a/clang/test/Driver/extend-variable-liveness.c
+++ b/clang/test/Driver/extend-variable-liveness.c
@@ -1,8 +1,7 @@
 // Tests that -fextend-variable-liveness and its aliases are correctly passed
-// by the driver, and are set by default at -Og.
+// by the driver.
 
 // RUN: %clang -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,DEFAULT
-// RUN: %clang -### -Og -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,ALL
 // RUN: %clang -fextend-variable-liveness=none -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,NONE
 // RUN: %clang -fextend-variable-liveness=this -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,THIS
 // RUN: %clang -fextend-variable-liveness=all -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,ALL