[WebAssembly] Rematerialize constants rather than hold them live in registers.

Teach the register stackifier to rematerialize constants that have multiple
uses instead of leaving them in registers. In the WebAssembly encoding, it's
the same code size to materialize most constants as it is to read a value
from a register.

llvm-svn: 258142

1 files changed, 20 insertions, 6 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
index 028e9af..37dd0c4 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
@@ -32,6 +32,21 @@ WebAssemblyInstrInfo::WebAssemblyInstrInfo(const WebAssemblySubtarget &STI)
                               WebAssembly::ADJCALLSTACKUP),
       RI(STI.getTargetTriple()) {}
 
+bool WebAssemblyInstrInfo::isReallyTriviallyReMaterializable(
+    const MachineInstr *MI, AliasAnalysis *AA) const {
+  switch (MI->getOpcode()) {
+  case WebAssembly::CONST_I32:
+  case WebAssembly::CONST_I64:
+  case WebAssembly::CONST_F32:
+  case WebAssembly::CONST_F64:
+    // isReallyTriviallyReMaterializableGeneric misses these because of the
+    // ARGUMENTS implicit def, so we manualy override it here.
+    return true;
+  default:
+    return false;
+  }
+}
+
 void WebAssemblyInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
                                        MachineBasicBlock::iterator I,
                                        DebugLoc DL, unsigned DestReg,
@@ -39,9 +54,10 @@ void WebAssemblyInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
   // This method is called by post-RA expansion, which expects only pregs to
   // exist. However we need to handle both here.
   auto &MRI = MBB.getParent()->getRegInfo();
-  const TargetRegisterClass *RC = TargetRegisterInfo::isVirtualRegister(DestReg) ?
-      MRI.getRegClass(DestReg) :
-      MRI.getTargetRegisterInfo()->getMinimalPhysRegClass(SrcReg);
+  const TargetRegisterClass *RC =
+      TargetRegisterInfo::isVirtualRegister(DestReg)
+          ? MRI.getRegClass(DestReg)
+          : MRI.getTargetRegisterInfo()->getMinimalPhysRegClass(SrcReg);
 
   unsigned CopyLocalOpcode;
   if (RC == &WebAssembly::I32RegClass)
@@ -145,9 +161,7 @@ unsigned WebAssemblyInstrInfo::InsertBranch(MachineBasicBlock &MBB,
   assert(Cond.size() == 2 && "Expected a flag and a successor block");
 
   if (Cond[0].getImm()) {
-    BuildMI(&MBB, DL, get(WebAssembly::BR_IF))
-        .addOperand(Cond[1])
-        .addMBB(TBB);
+    BuildMI(&MBB, DL, get(WebAssembly::BR_IF)).addOperand(Cond[1]).addMBB(TBB);
   } else {
     BuildMI(&MBB, DL, get(WebAssembly::BR_UNLESS))
         .addOperand(Cond[1])