[llvm] r193535 - Return early from getUnconditionalBranchTargetOpValue if the branch target is

[Lang Hames]

Author: lhames
Date: Mon Oct 28 15:51:11 2013
New Revision: 193535

URL: http://llvm.org/viewvc/llvm-project?rev=193535&view=rev
Log:
Return early from getUnconditionalBranchTargetOpValue if the branch target is
an MCExpr, in order to avoid writing an encoded zero value in the immediate
field.

When getUnconditionalBranchTargetOpValue is called with an MCExpr target, we
don't know what the final immediate field value should be. We shouldn't
explicitly set the immediate field to an encoded zero value as zero is encoded
with a non-zero bit pattern. This leads to bits being set that pollute the
final immediate value. The nature of the encoding is such that the polluted
bits only affect very large immediate values, explaining why this hasn't
caused problems earlier.

Fixes <rdar://problem/15155975>.


Modified:
    llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
    llvm/trunk/test/MC/ARM/basic-thumb2-instructions.s

Modified: llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp?rev=193535&r1=193534&r2=193535&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp (original)
+++ llvm/trunk/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp Mon Oct 28 15:51:11 2013
@@ -641,7 +641,7 @@ getUnconditionalBranchTargetOpValue(cons
   const MCOperand MO = MI.getOperand(OpIdx);
     
   if(MO.isExpr())
-    Val = ::getBranchTargetOpValue(MI, OpIdx, ARM::fixup_t2_uncondbranch, Fixups);
+    return ::getBranchTargetOpValue(MI, OpIdx, ARM::fixup_t2_uncondbranch, Fixups);
   else 
     Val = MO.getImm() >> 1;
 

Modified: llvm/trunk/test/MC/ARM/basic-thumb2-instructions.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ARM/basic-thumb2-instructions.s?rev=193535&r1=193534&r2=193535&view=diff
==============================================================================
--- llvm/trunk/test/MC/ARM/basic-thumb2-instructions.s (original)
+++ llvm/trunk/test/MC/ARM/basic-thumb2-instructions.s Mon Oct 28 15:51:11 2013
@@ -226,12 +226,12 @@ _func:
         beq.w _bar
         bmi.w   #-183396
 
-@ CHECK: b.w	_bar                    @ encoding: [A,0xf0'A',A,0xb8'A']
+@ CHECK: b.w	_bar                    @ encoding: [A,0xf0'A',A,0x90'A']
           @   fixup A - offset: 0, value: _bar, kind: fixup_t2_uncondbranch
 @ CHECK: beq.w	_bar                    @ encoding: [A,0xf0'A',A,0x80'A']
           @   fixup A - offset: 0, value: _bar, kind: fixup_t2_condbranch
 @ CHECK: it	eq                      @ encoding: [0x08,0xbf]
-@ CHECK: beq.w	_bar                    @ encoding: [A,0xf0'A',A,0xb8'A']
+@ CHECK: beq.w	_bar                    @ encoding: [A,0xf0'A',A,0x90'A']
           @   fixup A - offset: 0, value: _bar, kind: fixup_t2_uncondbranch
 @ CHECK: bmi.w   #-183396                @ encoding: [0x13,0xf5,0xce,0xa9]