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[clang][ARM] disable frame pointers by default for bare metal ARM targets (#117140)
because: - This brings Clang in line with GCC for which this is the default for ARM - It frees up a register, so performance increase, especially on Thumb/6-M - It will decrease code size
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5 files changed

+80
-23
lines changed

5 files changed

+80
-23
lines changed

‎clang/lib/Driver/ToolChains/Arch/ARM.cpp

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -52,6 +52,26 @@ bool arm::isARMAProfile(const llvm::Triple &Triple) {
5252
return llvm::ARM::parseArchProfile(Arch) == llvm::ARM::ProfileKind::A;
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}
5454

55+
/// Is the triple {arm,armeb,thumb,thumbeb}-none-none-{eabi,eabihf} ?
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bool arm::isARMEABIBareMetal(const llvm::Triple &Triple) {
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auto arch = Triple.getArch();
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if (arch != llvm::Triple::arm && arch != llvm::Triple::thumb &&
59+
arch != llvm::Triple::armeb && arch != llvm::Triple::thumbeb)
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return false;
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62+
if (Triple.getVendor() != llvm::Triple::UnknownVendor)
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return false;
64+
65+
if (Triple.getOS() != llvm::Triple::UnknownOS)
66+
return false;
67+
68+
if (Triple.getEnvironment() != llvm::Triple::EABI &&
69+
Triple.getEnvironment() != llvm::Triple::EABIHF)
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return false;
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72+
return true;
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}
74+
5575
// Get Arch/CPU from args.
5676
void arm::getARMArchCPUFromArgs(const ArgList &Args, llvm::StringRef &Arch,
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llvm::StringRef &CPU, bool FromAs) {

‎clang/lib/Driver/ToolChains/Arch/ARM.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -75,6 +75,7 @@ int getARMSubArchVersionNumber(const llvm::Triple &Triple);
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bool isARMMProfile(const llvm::Triple &Triple);
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bool isARMAProfile(const llvm::Triple &Triple);
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bool isARMBigEndian(const llvm::Triple &Triple, const llvm::opt::ArgList &Args);
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bool isARMEABIBareMetal(const llvm::Triple &Triple);
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} // end namespace arm
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} // end namespace tools

‎clang/lib/Driver/ToolChains/BareMetal.cpp

Lines changed: 2 additions & 23 deletions
Original file line numberDiff line numberDiff line change
@@ -128,27 +128,6 @@ BareMetal::BareMetal(const Driver &D, const llvm::Triple &Triple,
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}
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}
130130

131-
/// Is the triple {arm,armeb,thumb,thumbeb}-none-none-{eabi,eabihf} ?
132-
static bool isARMBareMetal(const llvm::Triple &Triple) {
133-
if (Triple.getArch() != llvm::Triple::arm &&
134-
Triple.getArch() != llvm::Triple::thumb &&
135-
Triple.getArch() != llvm::Triple::armeb &&
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Triple.getArch() != llvm::Triple::thumbeb)
137-
return false;
138-
139-
if (Triple.getVendor() != llvm::Triple::UnknownVendor)
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return false;
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142-
if (Triple.getOS() != llvm::Triple::UnknownOS)
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return false;
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145-
if (Triple.getEnvironment() != llvm::Triple::EABI &&
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Triple.getEnvironment() != llvm::Triple::EABIHF)
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return false;
148-
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return true;
150-
}
151-
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/// Is the triple {aarch64.aarch64_be}-none-elf?
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static bool isAArch64BareMetal(const llvm::Triple &Triple) {
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if (Triple.getArch() != llvm::Triple::aarch64 &&
@@ -267,7 +246,7 @@ void BareMetal::findMultilibs(const Driver &D, const llvm::Triple &Triple,
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}
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bool BareMetal::handlesTarget(const llvm::Triple &Triple) {
270-
return isARMBareMetal(Triple) || isAArch64BareMetal(Triple) ||
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return arm::isARMEABIBareMetal(Triple) || isAArch64BareMetal(Triple) ||
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isRISCVBareMetal(Triple) || isPPCBareMetal(Triple);
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}
273252

@@ -561,7 +540,7 @@ void baremetal::Linker::ConstructJob(Compilation &C, const JobAction &JA,
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// The R_ARM_TARGET2 relocation must be treated as R_ARM_REL32 on arm*-*-elf
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// and arm*-*-eabi (the default is R_ARM_GOT_PREL, used on arm*-*-linux and
563542
// arm*-*-*bsd).
564-
if (isARMBareMetal(TC.getTriple()))
543+
if (arm::isARMEABIBareMetal(TC.getTriple()))
565544
CmdArgs.push_back("--target2=rel");
566545

567546
CmdArgs.push_back("-o");

‎clang/lib/Driver/ToolChains/CommonArgs.cpp

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -19,6 +19,7 @@
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#include "Arch/SystemZ.h"
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#include "Arch/VE.h"
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#include "Arch/X86.h"
22+
#include "BareMetal.h"
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#include "HIPAMD.h"
2324
#include "Hexagon.h"
2425
#include "MSP430.h"
@@ -151,6 +152,9 @@ static bool useFramePointerForTargetByDefault(const llvm::opt::ArgList &Args,
151152
}
152153
}
153154

155+
if (arm::isARMEABIBareMetal(Triple))
156+
return false;
157+
154158
return true;
155159
}
156160

‎clang/test/Driver/frame-pointer-elim.c

Lines changed: 53 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -162,5 +162,58 @@
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// RUN: FileCheck --check-prefix=KEEP-NON-LEAF %s
163163
// RUN: not %clang -### --target=riscv64-linux-android -mbig-endian -O1 -S %s 2>&1 | \
164164
// RUN: FileCheck --check-prefix=KEEP-NON-LEAF %s
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166+
// On ARM backend bare metal targets, frame pointer is omitted
167+
// RUN: %clang -### --target=arm-arm-none-eabi -S %s 2>&1 | \
168+
// RUN: FileCheck --check-prefix=KEEP-NONE %s
169+
// RUN: %clang -### --target=arm-arm-none-eabihf -S %s 2>&1 | \
170+
// RUN: FileCheck --check-prefix=KEEP-NONE %s
171+
// RUN: %clang -### --target=arm-arm-none-eabi -S -fno-omit-frame-pointer %s 2>&1 | \
172+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
173+
// RUN: %clang -### --target=arm-arm-none-eabihf -S -fno-omit-frame-pointer %s 2>&1 | \
174+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
175+
// RUN: %clang -### --target=arm-arm-none-eabi -S -O1 %s 2>&1 | \
176+
// RUN: FileCheck --check-prefix=KEEP-NONE %s
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// RUN: %clang -### --target=arm-arm-none-eabihf -S -O1 %s 2>&1 | \
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// RUN: FileCheck --check-prefix=KEEP-NONE %s
179+
// RUN: %clang -### --target=arm-arm-none-eabi -S -O1 -fno-omit-frame-pointer %s 2>&1 | \
180+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
181+
// RUN: %clang -### --target=arm-arm-none-eabihf -S -O1 -fno-omit-frame-pointer %s 2>&1 | \
182+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
183+
// RUN: %clang -### --target=armeb-arm-none-eabi -S %s 2>&1 | \
184+
// RUN: FileCheck --check-prefix=KEEP-NONE %s
185+
// RUN: %clang -### --target=thumb-arm-none-eabi -S %s 2>&1 | \
186+
// RUN: FileCheck --check-prefix=KEEP-NONE %s
187+
// RUN: %clang -### --target=thumbeb-arm-none-eabi -S %s 2>&1 | \
188+
// RUN: FileCheck --check-prefix=KEEP-NONE %s
189+
190+
// Check that for Apple bare metal targets, we're keeping frame pointers by default
191+
// RUN: %clang -### --target=thumbv6m-apple-none-macho -S %s 2>&1 | \
192+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
193+
// RUN: %clang -### --target=thumbv6m-apple-none-macho -S -fno-omit-frame-pointer %s 2>&1 | \
194+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
195+
// RUN: %clang -### --target=arm-apple-none-macho -S %s 2>&1 | \
196+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
197+
// RUN: %clang -### --target=arm-apple-none-macho -S -fno-omit-frame-pointer %s 2>&1 | \
198+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
199+
// RUN: %clang -### --target=thumbv6m-apple-none-macho -S -O1 %s 2>&1 | \
200+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
201+
// RUN: %clang -### --target=thumbv6m-apple-none-macho -S -O1 -fno-omit-frame-pointer %s 2>&1 | \
202+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
203+
// RUN: %clang -### --target=arm-apple-none-macho -S -O1 %s 2>&1 | \
204+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
205+
// RUN: %clang -### --target=arm-apple-none-macho -S -O1 -fno-omit-frame-pointer %s 2>&1 | \
206+
// RUN: FileCheck --check-prefix=KEEP-ALL %s
207+
208+
// AArch64 bare metal targets behave like hosted targets
209+
// RUN: %clang -### --target=aarch64-none-elf -S %s 2>&1 | \
210+
// RUN: FileCheck --check-prefix=KEEP-NON-LEAF %s
211+
// RUN: %clang -### --target=aarch64-none-elf -S -O1 %s 2>&1 | \
212+
// RUN: FileCheck --check-prefix=KEEP-NON-LEAF %s
213+
// RUN: %clang -### --target=aarch64-none-elf -S -fno-omit-frame-pointer %s 2>&1 | \
214+
// RUN: FileCheck --check-prefix=KEEP-NON-LEAF %s
215+
// RUN: %clang -### --target=aarch64-none-elf -S -O1 -fno-omit-frame-pointer %s 2>&1 | \
216+
// RUN: FileCheck --check-prefix=KEEP-NON-LEAF %s
217+
165218
void f0() {}
166219
void f1() { f0(); }

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