IssueTracker

Forked from bug 187790592 (comment 32). If you read closely you can see that when I tried to use the -mno-omit-leaf-frame-pointer it didn't work.

Repeating the test and adding -frecord-gcc-switches:

Compile my test with:

armv7a-cros-linux-gnueabihf-clang \
  -mthumb -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -O2 \
  testcase.c -o bug1040659-clang-thumb-fp-leaf \
  -frecord-gcc-switches

armv7a-cros-linux-gnueabihf-clang \
  -mthumb -fno-omit-frame-pointer -O2 \
  testcase.c -o bug1040659-clang-thumb-fp \
  -frecord-gcc-switches

Check and see that there's no difference:

$ armv7a-cros-linux-gnueabi-objdump -dRS bug1040659-clang-thumb-fp > bug1040659-clang-thumb-fp.dis.txt
$ armv7a-cros-linux-gnueabi-objdump -dRS bug1040659-clang-thumb-fp-leaf > bug1040659-clang-thumb-fp-leaf.dis.txt

$ diff bug1040659-clang-thumb-fp.dis.txt bug1040659-clang-thumb-fp-leaf.dis.txt
2c2
< bug1040659-clang-thumb-fp:     file format elf32-littlearm
---
> bug1040659-clang-thumb-fp-leaf:     file format elf32-littlearm

$ readelf -p .GCC.command.line bug1040659-clang-thumb-fp

String dump of section '.GCC.command.line':
  [     0]  /usr/bin/clang-12 --sysroot=/usr/armv7a-cros-linux-gnueabihf -Qunused-arguments -fno-addrsig -fdebug-default-version=5 -Wno-tautological-constant-compare -Wno-tautological-unsigned-enum-zero-compare -Wno-unknown-warning-option -Wno-section -static-libgcc -fuse-ld=lld -Wno-final-dtor-non-final-class -Werror=poison-system-directories -fexperimental-new-pass-manager -Wno-compound-token-split-by-macro -fcrash-diagnostics-dir=/tmp/clang_crash_diagnostics -fcommon -fstack-protector-strong -fPIE -pie -D _FORTIFY_SOURCE=2 -mthumb -mthumb -fno-omit-frame-pointer -O2 testcase.c -o bug1040659-clang-thumb-fp -frecord-command-line -Wno-implicit-int-float-conversion -Wno-compound-token-split-by-space -Wno-string-concatenation -B ../../../../usr/libexec/gcc/armv7a-cros-linux-gnueabihf --target=armv7a-cros-linux-gnueabihf

$ readelf -p .GCC.command.line bug1040659-clang-thumb-fp-leaf

String dump of section '.GCC.command.line':
  [     0]  /usr/bin/clang-12 --sysroot=/usr/armv7a-cros-linux-gnueabihf -Qunused-arguments -fno-addrsig -fdebug-default-version=5 -Wno-tautological-constant-compare -Wno-tautological-unsigned-enum-zero-compare -Wno-unknown-warning-option -Wno-section -static-libgcc -fuse-ld=lld -Wno-final-dtor-non-final-class -Werror=poison-system-directories -fexperimental-new-pass-manager -Wno-compound-token-split-by-macro -fcrash-diagnostics-dir=/tmp/clang_crash_diagnostics -fcommon -fstack-protector-strong -fPIE -pie -D _FORTIFY_SOURCE=2 -mthumb -mthumb -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -O2 testcase.c -o bug1040659-clang-thumb-fp-leaf -frecord-command-line -Wno-implicit-int-float-conversion -Wno-compound-token-split-by-space -Wno-string-concatenation -B ../../../../usr/libexec/gcc/armv7a-cros-linux-gnueabihf --target=armv7a-cros-linux-gnueabihf

And just to see one of the functions:

void __attribute__((noinline)) leaf1(unsigned long long count)
{
        while (count--) {
                scratchpad ^= 0x1;
        }
}

0000069c <leaf1>:
 69c:   ea50 0201       orrs.w  r2, r0, r1
 6a0:   bf08            it      eq
 6a2:   4770            bxeq    lr
 6a4:   4a06            ldr     r2, [pc, #24]   ; (6c0 <leaf1+0x24>)
 6a6:   447a            add     r2, pc
 6a8:   6813            ldr     r3, [r2, #0]
 6aa:   3801            subs    r0, #1
 6ac:   f161 0100       sbc.w   r1, r1, #0
 6b0:   f083 0301       eor.w   r3, r3, #1
 6b4:   6013            str     r3, [r2, #0]
 6b6:   ea50 0301       orrs.w  r3, r0, r1
 6ba:   d1f5            bne.n   6a8 <leaf1+0xc>
 6bc:   4770            bx      lr
 6be:   bf00            nop
 6c0:   000206a6        .word   0x000206a6