[PATCH] D21919: AMDGPU: Make infinite loop clear, NFC

[Duncan P. N. Exon Smith via llvm-commits]

dexonsmith created this revision.
dexonsmith added a reviewer: arsenm.
dexonsmith added a subscriber: llvm-commits.
Herald added a reviewer: tstellarAMD.
Herald added subscribers: kzhuravl, arsenm.

Change a while loop that was checking for nullptr on an 
iterator-to-pointer conversion to an infinite for loop.  Now it's clear
that the condition doesn't terminate.

The only change in behaviour is if an invalid iterator (holding nullptr)
was passed into AMDGPUCFGStructurizer::reversePredicateSetter.  There
are only two callers, and they both dereference the iterator before
sending it in, so rather than adding an early return to avoid the loop
I've just asserted (using a static_cast, to avoid an implicit conversion
to pointer).


http://reviews.llvm.org/D21919

Files:
  lib/Target/AMDGPU/AMDILCFGStructurizer.cpp

Index: lib/Target/AMDGPU/AMDILCFGStructurizer.cpp
===================================================================
--- lib/Target/AMDGPU/AMDILCFGStructurizer.cpp
+++ lib/Target/AMDGPU/AMDILCFGStructurizer.cpp
@@ -423,7 +423,8 @@
 
 void AMDGPUCFGStructurizer::reversePredicateSetter(
     MachineBasicBlock::iterator I) {
-  while (I--) {
+  assert(static_cast<MachineInstr *>(I) && "Expected valid iterator");
+  for (;; --I) {
     if (I->getOpcode() == AMDGPU::PRED_X) {
       switch (static_cast<MachineInstr *>(I)->getOperand(2).getImm()) {
       case OPCODE_IS_ZERO_INT:


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