[mips] Compact branch policy control for MIPSR6
This patch adds the commandline option -mips-compact-branches={never,optimal,always),
which controls how LLVM generates compact branches for MIPS targets. By
default, the compact branch policy is 'optimal' where LLVM will (hopefully)
pick the optimal branch for any situation. The 'never' policy will disable
the generation of compact branches and 'always' will generate compact branches
wherever possible.
Reviewers: dsanders
Differential Review: http://reviews.llvm.org/D20167
llvm-svn: 269753
diff --git a/llvm/lib/Target/Mips/MipsDelaySlotFiller.cpp b/llvm/lib/Target/Mips/MipsDelaySlotFiller.cpp
index 0a7ffb1..0a84f08 100644
--- a/llvm/lib/Target/Mips/MipsDelaySlotFiller.cpp
+++ b/llvm/lib/Target/Mips/MipsDelaySlotFiller.cpp
@@ -62,6 +62,28 @@
cl::desc("Disallow MIPS delay filler to search backward."),
cl::Hidden);
+enum CompactBranchPolicy {
+ CB_Never, ///< The policy 'never' may in some circumstances or for some
+ ///< ISAs not be absolutely adhered to.
+ CB_Optimal, ///< Optimal is the default and will produce compact branches
+ ///< when delay slots cannot be filled.
+ CB_Always ///< 'always' may in some circumstances may not be
+ ///< absolutely adhered to there may not be a corresponding
+ ///< compact form of a branch.
+};
+
+static cl::opt<CompactBranchPolicy> MipsCompactBranchPolicy(
+ "mips-compact-branches",cl::Optional,
+ cl::init(CB_Optimal),
+ cl::desc("MIPS Specific: Compact branch policy."),
+ cl::values(
+ clEnumValN(CB_Never, "never", "Do not use compact branches if possible."),
+ clEnumValN(CB_Optimal, "optimal", "Use compact branches where appropiate (default)."),
+ clEnumValN(CB_Always, "always", "Always use compact branches if possible."),
+ clEnumValEnd
+ )
+);
+
namespace {
typedef MachineBasicBlock::iterator Iter;
typedef MachineBasicBlock::reverse_iterator ReverseIter;
@@ -563,14 +585,17 @@
if (!DisableDelaySlotFiller && (TM.getOptLevel() != CodeGenOpt::None)) {
bool Filled = false;
- if (searchBackward(MBB, I)) {
- Filled = true;
- } else if (I->isTerminator()) {
- if (searchSuccBBs(MBB, I)) {
+ if (MipsCompactBranchPolicy.getValue() != CB_Always ||
+ !TII->getEquivalentCompactForm(I)) {
+ if (searchBackward(MBB, I)) {
+ Filled = true;
+ } else if (I->isTerminator()) {
+ if (searchSuccBBs(MBB, I)) {
+ Filled = true;
+ }
+ } else if (searchForward(MBB, I)) {
Filled = true;
}
- } else if (searchForward(MBB, I)) {
- Filled = true;
}
if (Filled) {
@@ -596,8 +621,9 @@
// For MIPSR6 attempt to produce the corresponding compact (no delay slot)
// form of the CTI. For indirect jumps this will not require inserting a
// NOP and for branches will hopefully avoid requiring a NOP.
- if ((InMicroMipsMode || STI.hasMips32r6()) &&
- TII->getEquivalentCompactForm(I)) {
+ if ((InMicroMipsMode ||
+ (STI.hasMips32r6() && MipsCompactBranchPolicy != CB_Never)) &&
+ TII->getEquivalentCompactForm(I)) {
I = replaceWithCompactBranch(MBB, I, I->getDebugLoc());
continue;
}