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AMDGPU/SI: Make comments more precise. 

True branch instructions do behave as expected with liveness.

Avoid the phrasing "branch decision is based on a value in an SGPR"
because this could be misleading. A VALU compare instruction's
result is still based on an SGPR, even though that condition
may be divergent.

llvm-svn: 245131
This commit is contained in:
Matt Arsenault 2015-08-15 00:12:30 +00:00
parent 650cc3dfd6
commit 4275c29a02
1 changed files with 8 additions and 8 deletions
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16
llvm/lib/Target/AMDGPU/SIFixSGPRLiveRanges.cpp
View File

@ -7,9 +7,8 @@
//
//===----------------------------------------------------------------------===//
//
/// \file
/// SALU instructions ignore control flow, so we need to modify the live ranges
/// of the registers they define in some cases.
/// \file SALU instructions ignore the execution mask, so we need to modify the
/// live ranges of the registers they define in some cases.
///
/// The main case we need to handle is when a def is used in one side of a
/// branch and not another. For example:
@ -138,7 +137,8 @@ bool SIFixSGPRLiveRanges::runOnMachineFunction(MachineFunction &MF) {
if (MBB.succ_size() < 2)
continue;
// We have structured control flow, so number of successors should be two.
// We have structured control flow, so the number of successors should be
// two.
assert(MBB.succ_size() == 2);
MachineBasicBlock *SuccA = *MBB.succ_begin();
MachineBasicBlock *SuccB = *(++MBB.succ_begin());
@ -161,10 +161,10 @@ bool SIFixSGPRLiveRanges::runOnMachineFunction(MachineFunction &MF) {
unsigned Reg = RegLR.first;
LiveRange *LR = RegLR.second;
// FIXME: We could be smarter here. If the register is Live-In to
// one block, but the other doesn't have any SGPR defs, then there
// won't be a conflict. Also, if the branch decision is based on
// a value in an SGPR, then there will be no conflict.
// FIXME: We could be smarter here. If the register is Live-In to one
// block, but the other doesn't have any SGPR defs, then there won't be a
// conflict. Also, if the branch condition is uniform then there will be
// no conflict.
bool LiveInToA = LIS->isLiveInToMBB(*LR, SuccA);
bool LiveInToB = LIS->isLiveInToMBB(*LR, SuccB);