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R600/SI: Move PHIs that define SGPRs to the VALU in most cases 

This fixes a bug that is uncovered by a future commit and will
be tested by the test/CodeGen/R600/sgpr-control-flow.ll test case.

llvm-svn: 218352
This commit is contained in:
Tom Stellard 2014-09-24 01:33:26 +00:00
parent 60024a0558
commit deb3f9e643
1 changed files with 52 additions and 0 deletions
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52
llvm/lib/Target/R600/SIFixSGPRCopies.cpp
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@ -238,14 +238,66 @@ bool SIFixSGPRCopies::runOnMachineFunction(MachineFunction &MF) {
// If a PHI node defines an SGPR and any of its operands are VGPRs,
// then we need to move it to the VALU.
//
// Also, if a PHI node defines an SGPR and has all SGPR operands
// we must move it to the VALU, because the SGPR operands will
// all end up being assigned the same register, which means
// there is a potential for a conflict if different threads take
// different control flow paths.
//
// For Example:
//
// sgpr0 = def;
// ...
// sgpr1 = def;
// ...
// sgpr2 = PHI sgpr0, sgpr1
// use sgpr2;
//
// Will Become:
//
// sgpr2 = def;
// ...
// sgpr2 = def;
// ...
// use sgpr2
//
// FIXME: This is OK if the branching decision is made based on an
// SGPR value.
bool SGPRBranch = false;
// The one exception to this rule is when one of the operands
// is defined by a SI_BREAK, SI_IF_BREAK, or SI_ELSE_BREAK
// instruction. In this case, there we know the program will
// never enter the second block (the loop) without entering
// the first block (where the condition is computed), so there
// is no chance for values to be over-written.
bool HasBreakDef = false;
for (unsigned i = 1; i < MI.getNumOperands(); i+=2) {
unsigned Reg = MI.getOperand(i).getReg();
if (TRI->hasVGPRs(MRI.getRegClass(Reg))) {
TII->moveToVALU(MI);
break;
}
MachineInstr *DefInstr = MRI.getUniqueVRegDef(Reg);
assert(DefInstr);
switch(DefInstr->getOpcode()) {
case AMDGPU::SI_BREAK:
case AMDGPU::SI_IF_BREAK:
case AMDGPU::SI_ELSE_BREAK:
// If we see a PHI instruction that defines an SGPR, then that PHI
// instruction has already been considered and should have
// a *_BREAK as an operand.
case AMDGPU::PHI:
HasBreakDef = true;
break;
}
}
if (!SGPRBranch && !HasBreakDef)
TII->moveToVALU(MI);
break;
}
case AMDGPU::REG_SEQUENCE: {