[clang] [llvm] [Clang] Cleanup docs and comments relating to -fextend-variable-liveness (PR #124767)
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Tue Jan 28 07:30:06 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-driver
Author: Stephen Tozer (SLTozer)
<details>
<summary>Changes</summary>
This patch contains a number of changes relating to the above flag; primarily it updates comment references to the old flag names, "-fextend-lifetimes" and "-fextend-this-ptr" to refer to the new names, "-fextend-variable-liveness[={all,this}]". These changes are all NFC.
This patch also removes the explicit -fextend-this-ptr-liveness flag alias, and shortens the help-text for the main flag; these are both changes that were meant to be applied in the initial PR (#<!-- -->110000), but due to some user-error on my part they were not included in the merged commit.
---
Full diff: https://github.com/llvm/llvm-project/pull/124767.diff
14 Files Affected:
- (modified) clang/docs/ReleaseNotes.rst (+8-8)
- (modified) clang/include/clang/Driver/Options.td (+1-9)
- (modified) clang/lib/CodeGen/CGDecl.cpp (+1-1)
- (modified) clang/lib/CodeGen/CodeGenFunction.h (+2-2)
- (modified) clang/test/CodeGen/fake-use-sanitizer.cpp (+1-1)
- (modified) clang/test/CodeGen/fake-use-this.cpp (+1-1)
- (modified) clang/test/Driver/extend-variable-liveness.c (-1)
- (modified) llvm/test/CodeGen/MIR/X86/fake-use-tailcall.mir (+1-1)
- (modified) llvm/test/CodeGen/X86/fake-use-simple-tail-call.ll (+1-1)
- (modified) llvm/test/CodeGen/X86/fake-use-zero-length.ll (+1-1)
- (modified) llvm/test/DebugInfo/AArch64/fake-use-global-isel.ll (+1-1)
- (modified) llvm/test/DebugInfo/X86/fake-use.ll (+1-1)
- (modified) llvm/test/Transforms/CodeGenPrepare/X86/fake-use-split-ret.ll (+1-1)
- (modified) llvm/test/Transforms/GVN/fake-use-constprop.ll (+1-1)
``````````diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index c5a5da5daf8f5e..cf694310c79f62 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -525,14 +525,14 @@ New Compiler Flags
through optimizations, meaning that variables will typically be visible in a
debugger more often. The flag has two levels: ``-fextend-variable-liveness``,
or ``-fextend-variable-liveness=all``, extendes the liveness of all user
- variables and the ``this`` pointer. Alternatively ``-fextend-this-ptr``, or
- ``-fextend-variable-liveness=this``, has the same behaviour but applies only
- to the ``this`` variable in C++ class member functions, meaning its effect is
- a strict subset of ``-fextend-variable-liveness``. Note that this flag
- modifies the results of optimizations that Clang performs, which will result
- in reduced performance in generated code; however, this feature will not
- extend the liveness of some variables in cases where doing so would likely
- have a severe impact on generated code performance.
+ variables and the ``this`` pointer. Alternatively
+ ``-fextend-variable-liveness=this`` has the same behaviour but applies only to
+ the ``this`` variable in C++ class member functions, meaning its effect is a
+ strict subset of ``-fextend-variable-liveness``. Note that this flag modifies
+ the results of optimizations that Clang performs, which will result in reduced
+ performance in generated code; however, this feature will not extend the
+ liveness of some variables in cases where doing so would likely have a severe
+ impact on generated code performance.
- The ``-Warray-compare`` warning has been added to warn about array comparison
on versions older than C++20.
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 6fa8a8273aca34..2bf687895db294 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -4352,19 +4352,11 @@ def stack_usage_file : Separate<["-"], "stack-usage-file">,
def fextend_variable_liveness_EQ : Joined<["-"], "fextend-variable-liveness=">,
Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
HelpText<"Extend the liveness of user variables through optimizations to "
- "prevent stale or optimized-out variable values when debugging. Can "
- "be applied to all user variables, or just to the C++ 'this' ptr. "
- "May choose not to extend the liveness of some variables, such as "
- "non-scalars larger than 4 unsigned ints, or variables in any "
- "inlined functions.">,
+ "prevent stale or optimized-out variable values when debugging."
Values<"all,this,none">,
NormalizedValues<["All", "This", "None"]>,
NormalizedValuesScope<"CodeGenOptions::ExtendVariableLivenessKind">,
MarshallingInfoEnum<CodeGenOpts<"ExtendVariableLiveness">, "None">;
-def fextend_this_ptr_liveness : Flag<["-"], "fextend-this-ptr-liveness">,
- Visibility<[ClangOption, CC1Option]>,
- Alias<fextend_variable_liveness_EQ>, AliasArgs<["this"]>,
- HelpText<"Alias for -fextend-variable-liveness=this.">;
def fextend_variable_liveness : Flag<["-"], "fextend-variable-liveness">,
Visibility<[ClangOption, CC1Option]>,
Alias<fextend_variable_liveness_EQ>, AliasArgs<["all"]>,
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index e0d2048262f8f1..747e420d031b6f 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1423,7 +1423,7 @@ void CodeGenFunction::EmitAndRegisterVariableArrayDimensions(
}
/// Return the maximum size of an aggregate for which we generate a fake use
-/// intrinsic when -fextend-lifetimes is in effect.
+/// intrinsic when -fextend-variable-liveness is in effect.
static uint64_t maxFakeUseAggregateSize(const ASTContext &C) {
return 4 * C.getTypeSize(C.UnsignedIntTy);
}
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 60f16a364d90d1..e978cad4336238 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -724,8 +724,8 @@ class CodeGenFunction : public CodeGenTypeCache {
};
// We are using objects of this 'cleanup' class to emit fake.use calls
- // for -fextend-lifetimes and -fextend-this-ptr. They are placed at the end of
- // a variable's scope analogous to lifetime markers.
+ // for -fextend-variable-liveness. They are placed at the end of a variable's
+ // scope analogous to lifetime markers.
class FakeUse final : public EHScopeStack::Cleanup {
Address Addr;
diff --git a/clang/test/CodeGen/fake-use-sanitizer.cpp b/clang/test/CodeGen/fake-use-sanitizer.cpp
index d544bf85d2d9e4..e808c645b9c60f 100644
--- a/clang/test/CodeGen/fake-use-sanitizer.cpp
+++ b/clang/test/CodeGen/fake-use-sanitizer.cpp
@@ -1,7 +1,7 @@
// RUN: %clang_cc1 %s -triple x86_64-unknown-linux-gnu -emit-llvm -fextend-variable-liveness -fsanitize=null -fsanitize-trap=null -o - | FileCheck --check-prefixes=CHECK,NULL --implicit-check-not=ubsantrap %s
// RUN: %clang_cc1 %s -triple x86_64-unknown-linux-gnu -emit-llvm -fextend-variable-liveness -o - | FileCheck %s
-// With -fextend-lifetimes, the compiler previously generated a fake.use of any
+// With -fextend-variable-liveness, the compiler previously generated a fake.use of any
// reference variable at the end of the scope in which its alloca exists. This
// caused two issues, where we would get fake uses for uninitialized variables
// if that variable was declared after an early-return, and UBSan's null checks
diff --git a/clang/test/CodeGen/fake-use-this.cpp b/clang/test/CodeGen/fake-use-this.cpp
index 2c49694b2cd4fd..c1725d88c7176a 100644
--- a/clang/test/CodeGen/fake-use-this.cpp
+++ b/clang/test/CodeGen/fake-use-this.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -emit-llvm -fextend-this-ptr-liveness -o - | FileCheck %s --implicit-check-not=fake.use
+// RUN: %clang_cc1 %s -emit-llvm -fextend-variable-liveness=this -o - | FileCheck %s --implicit-check-not=fake.use
// Check that we generate a fake_use call with the 'this' pointer as argument,
// and no other fake uses.
// The call should appear after the call to bar().
diff --git a/clang/test/Driver/extend-variable-liveness.c b/clang/test/Driver/extend-variable-liveness.c
index bdd89d6f7721ce..bbfb2ece6f297e 100644
--- a/clang/test/Driver/extend-variable-liveness.c
+++ b/clang/test/Driver/extend-variable-liveness.c
@@ -4,7 +4,6 @@
// RUN: %clang -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,DEFAULT
// 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-this-ptr-liveness -### -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
// RUN: %clang -fextend-variable-liveness -### -c %s 2>&1 | FileCheck %s --check-prefixes=CHECK,ALL
diff --git a/llvm/test/CodeGen/MIR/X86/fake-use-tailcall.mir b/llvm/test/CodeGen/MIR/X86/fake-use-tailcall.mir
index 6c2cb0e55222b2..3b833ae73551ab 100644
--- a/llvm/test/CodeGen/MIR/X86/fake-use-tailcall.mir
+++ b/llvm/test/CodeGen/MIR/X86/fake-use-tailcall.mir
@@ -8,7 +8,7 @@
# in the return block itself into the predecessor blocks. This test enures that we do so.
#
# Generated from the following source with
-# clang -fextend-lifetimes -S -emit-llvm -O2 -mllvm -stop-before=codegenprepare -o test.mir test.c
+# clang -fextend-variable-liveness -S -emit-llvm -O2 -mllvm -stop-before=codegenprepare -o test.mir test.c
#
# extern int f0();
# extern int f1();
diff --git a/llvm/test/CodeGen/X86/fake-use-simple-tail-call.ll b/llvm/test/CodeGen/X86/fake-use-simple-tail-call.ll
index 45a210ef391009..fb01da9f12c8b4 100644
--- a/llvm/test/CodeGen/X86/fake-use-simple-tail-call.ll
+++ b/llvm/test/CodeGen/X86/fake-use-simple-tail-call.ll
@@ -1,6 +1,6 @@
; RUN: llc < %s -mtriple=x86_64-unknown-unknown -O2 -o - \
; RUN: | FileCheck %s --implicit-check-not=TAILCALL
-; Generated with: clang -emit-llvm -O2 -S -fextend-lifetimes test.cpp -o -
+; Generated with: clang -emit-llvm -O2 -S -fextend-variable-liveness test.cpp -o -
; =========== test.cpp ===============
; extern int bar(int);
; int foo1(int i)
diff --git a/llvm/test/CodeGen/X86/fake-use-zero-length.ll b/llvm/test/CodeGen/X86/fake-use-zero-length.ll
index e3bdd2659dd913..71cb1029dcad65 100644
--- a/llvm/test/CodeGen/X86/fake-use-zero-length.ll
+++ b/llvm/test/CodeGen/X86/fake-use-zero-length.ll
@@ -4,7 +4,7 @@
; and structs. Check also that they are not propagated.
;
; Generated from the following source with
-; clang -fextend-lifetimes -S -emit-llvm -O2 -mllvm -stop-after=safe-stack -o test.mir test.cpp
+; clang -fextend-variable-liveness -S -emit-llvm -O2 -mllvm -stop-after=safe-stack -o test.mir test.cpp
;
; int main ()
; { int array[0]; }
diff --git a/llvm/test/DebugInfo/AArch64/fake-use-global-isel.ll b/llvm/test/DebugInfo/AArch64/fake-use-global-isel.ll
index 65a64583096959..2339b067c71e4f 100644
--- a/llvm/test/DebugInfo/AArch64/fake-use-global-isel.ll
+++ b/llvm/test/DebugInfo/AArch64/fake-use-global-isel.ll
@@ -12,7 +12,7 @@
; RUN: not %python %p/../Inputs/check-fake-use.py %t
; Generated with:
-; clang -O2 -g -S -emit-llvm -fextend-this-ptr fake-use.c
+; clang -O2 -g -S -emit-llvm -fextend-variable-liveness=this fake-use.c
;
; int glob[10];
; extern void bar();
diff --git a/llvm/test/DebugInfo/X86/fake-use.ll b/llvm/test/DebugInfo/X86/fake-use.ll
index 5ac5104a167118..0f24ab40ba9ad0 100644
--- a/llvm/test/DebugInfo/X86/fake-use.ll
+++ b/llvm/test/DebugInfo/X86/fake-use.ll
@@ -9,7 +9,7 @@
; RUN: not %python %p/../Inputs/check-fake-use.py %t
; Generated with:
-; clang -O2 -g -S -emit-llvm -fextend-this-ptr fake-use.c
+; clang -O2 -g -S -emit-llvm -fextend-variable-liveness=this fake-use.c
;
; int glob[10];
; extern void bar();
diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/fake-use-split-ret.ll b/llvm/test/Transforms/CodeGenPrepare/X86/fake-use-split-ret.ll
index b2cf89f6f2dd82..9f356b5e3cb427 100644
--- a/llvm/test/Transforms/CodeGenPrepare/X86/fake-use-split-ret.ll
+++ b/llvm/test/Transforms/CodeGenPrepare/X86/fake-use-split-ret.ll
@@ -2,7 +2,7 @@
;
; Ensure return instruction splitting ignores fake uses.
;
-; IR Generated with clang -O2 -S -emit-llvm -fextend-lifetimes test.cpp
+; IR Generated with clang -O2 -S -emit-llvm -fextend-variable-liveness test.cpp
;
;// test.cpp
;extern int bar(int);
diff --git a/llvm/test/Transforms/GVN/fake-use-constprop.ll b/llvm/test/Transforms/GVN/fake-use-constprop.ll
index 1466f9f9fca277..0e7ca101a2524a 100644
--- a/llvm/test/Transforms/GVN/fake-use-constprop.ll
+++ b/llvm/test/Transforms/GVN/fake-use-constprop.ll
@@ -7,7 +7,7 @@
; with respect to keeping the variable live up until the fake.use.
; This test checks that we don't generate any fake.uses with constant 0.
;
-; Reduced from the following test case, generated with clang -O2 -S -emit-llvm -fextend-lifetimes test.c
+; Reduced from the following test case, generated with clang -O2 -S -emit-llvm -fextend-variable-liveness test.c
;
; extern void func1();
; extern int bar();
``````````
</details>
https://github.com/llvm/llvm-project/pull/124767
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