[LLVMbugs] [Bug 16744] New: Clang optimized out a branch function with Os option

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16744

            Bug ID: 16744
           Summary: Clang optimized out a branch function with Os option
           Product: clang
           Version: 3.3
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mrcool0905 at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Created attachment 10954
  --> http://llvm.org/bugs/attachment.cgi?id=10954&action=edit
an example code

I Have some code like this. With Os option, I don't see any branching to
xQueueGenericSend in assembly. Clang 3.2 works correctly in this case.


(pxMutex->uxRecursiveCallCount)--;

if( pxMutex->uxRecursiveCallCount == 0 ) 
{   
    xQueueGenericSend( pxMutex, 0, queueMUTEX_GIVE_BLOCK_TIME);
    xReturn = pdPASS;
}

/usr/local/rui/toolchains/llvm/3.3/armv7m/bin/clang -mcpu=cortex-m4 -nostdinc
-isystem /usr/local/rui/toolchains/llvm/3.3/armv7m/lib/clang/3.3/include 
-mthumb -O2 -Os -c -o test.o test.c

The llvm bytecode generated with -S -emit-llvm: 

; ModuleID = 'test.c'
target datalayout =
"e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:64:128-a0:0:32-n32-S64"
target triple = "thumbv7em-none--eabi"

%struct.QueueDefinition = type { i8*, i8*, i8*, i8*, i32, i32, i32, i32, i32,
i8 }

; Function Attrs: nounwind optsize
define i32 @xQueueGiveMutexRecursive(%struct.QueueDefinition* nocapture
%pxMutex) #0 {
entry:
  %pcTail = getelementptr inbounds %struct.QueueDefinition* %pxMutex, i32 0,
i32 1
  %0 = load i8** %pcTail, align 4, !tbaa !0
  %call = tail call i8* @xTaskGetCurrentTaskHandle() #2
  %cmp = icmp eq i8* %0, %call
  br i1 %cmp, label %if.then, label %if.end5

if.then:                                          ; preds = %entry
  %pcReadFrom = getelementptr inbounds %struct.QueueDefinition* %pxMutex, i32
0, i32 3
  %1 = load i8** %pcReadFrom, align 4, !tbaa !0
  %incdec.ptr = getelementptr inbounds i8* %1, i32 -1
  store i8* %incdec.ptr, i8** %pcReadFrom, align 4, !tbaa !0
  br label %if.end5

if.end5:                                          ; preds = %entry, %if.then
  ret i32 0
}

; Function Attrs: optsize
declare i8* @xTaskGetCurrentTaskHandle() #1

attributes #0 = { nounwind optsize "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"="true"
"no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false"
"use-soft-float"="false" }
attributes #1 = { optsize "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"="true"
"no-infs-fp-math"="false" "no-nans-fp-math"="false" "unsafe-fp-math"="false"
"use-soft-float"="false" }
attributes #2 = { nounwind optsize }

!0 = metadata !{metadata !"any pointer", metadata !1}
!1 = metadata !{metadata !"omnipotent char", metadata !2}
!2 = metadata !{metadata !"Simple C/C++ TBAA"}



Disassembly of section .text:

00000000 <xQueueGiveMutexRecursive>:
   0:   b5b0            push    {r4, r5, r7, lr}
   2:   4604            mov     r4, r0
   4:   af02            add     r7, sp, #8
   6:   6865            ldr     r5, [r4, #4]
   8:   f7ff fffe       bl      0 <xTaskGetCurrentTaskHandle>
   c:   4285            cmp     r5, r0
   e:   bf02            ittt    eq
  10:   68e0            ldreq   r0, [r4, #12]
  12:   3801            subeq   r0, #1
  14:   60e0            streq   r0, [r4, #12]
  16:   2000            movs    r0, #0
  18:   bdb0            pop     {r4, r5, r7, pc}
  1a:   bf00            nop

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20130730/36894f54/attachment.html>