Combine allocas

src/IceTargetLoweringX86BaseImpl.h

Index: src/IceTargetLoweringX86BaseImpl.h
diff --git a/src/IceTargetLoweringX86BaseImpl.h b/src/IceTargetLoweringX86BaseImpl.h
index 56ee04d32e6510add168fd47871608b65c2cc9e2..0a6df2b12a3484defe01109b8b2b4317d730d39e 100644
--- a/src/IceTargetLoweringX86BaseImpl.h
+++ b/src/IceTargetLoweringX86BaseImpl.h
@@ -290,6 +290,10 @@ template <class Machine> void TargetX86Base<Machine>::staticInit() {
 template <class Machine> void TargetX86Base<Machine>::translateO2() {
   TimerMarker T(TimerStack::TT_O2, Func);
 
+  // Merge Alloca instructions, and lay out the stack.
+  Func->processAllocas();
+  Func->dump("After Alloca combining");
+
   if (!Ctx->getFlags().getPhiEdgeSplit()) {
     // Lower Phi instructions.
     Func->placePhiLoads();
@@ -957,6 +961,7 @@ void TargetX86Base<Machine>::lowerAlloca(const InstAlloca *Inst) {
   uint32_t Alignment =
       std::max(AlignmentParam, Traits::X86_STACK_ALIGNMENT_BYTES);
   if (Alignment > Traits::X86_STACK_ALIGNMENT_BYTES) {
+    setHasFramePointer();
     _and(esp, Ctx->getConstantInt32(-Alignment));
   }
   if (const auto *ConstantTotalSize =
@@ -5429,9 +5434,12 @@ Operand *TargetX86Base<Machine>::legalize(Operand *From, LegalMask Allowed,
     Variable *RegBase = nullptr;
     Variable *RegIndex = nullptr;
     if (Base) {
-      RegBase = legalizeToReg(Base);
+      RegBase = llvm::cast<Variable>(
+          legalize(Base, Legal_Reg | Legal_Rematerializable));
     }
     if (Index) {
+      RegIndex = llvm::cast<Variable>(
+          legalize(Index, Legal_Reg | Legal_Rematerializable));
       RegIndex = legalizeToReg(Index);

[Jim Stichnoth, 2015/11/11 17:39:45]

This statement eliminates the effect of the previous statement.  Which one do
you mean to keep?

[sehr, 2015/11/11 22:14:11]

Cursed cut/paste.  I wanted the rematerializable version, although it will fault
later if it happens and we don't use it today.

     }
     if (Base != RegBase || Index != RegIndex) {
@@ -5504,12 +5512,26 @@ Operand *TargetX86Base<Machine>::legalize(Operand *From, LegalMask Allowed,
     // either when the variable is pre-colored or when it is assigned infinite
     // weight.
     bool MustHaveRegister = (Var->hasReg() || Var->mustHaveReg());
+    bool MustRematerialize =
+        (Var->isRematerializable() && !(Allowed & Legal_Rematerializable));
     // We need a new physical register for the operand if:
-    //   Mem is not allowed and Var isn't guaranteed a physical
+    // - Mem is not allowed and Var isn't guaranteed a physical

[Jim Stichnoth, 2015/11/11 17:39:45]

reflow to 80-col

[sehr, 2015/11/11 22:14:11]

Done.

     //   register, or
-    //   RegNum is required and Var->getRegNum() doesn't match.
-    if ((!(Allowed & Legal_Mem) && !MustHaveRegister) ||
-        (RegNum != Variable::NoRegister && RegNum != Var->getRegNum())) {
+    // - RegNum is required and Var->getRegNum() doesn't match, or
+    // - Var is a rematerializable variable and rematerializable pass-through

[Jim Stichnoth, 2015/11/11 17:39:45]

reflow

[sehr, 2015/11/11 22:14:11]

Done.

+    //   is not allowed (in which case we need an lea instruction).
+    if (MustRematerialize) {
+      assert(Ty == IceType_i32);
+      Variable *NewVar = makeReg(Ty, RegNum);
+      // Since Var is rematerializable, the offset will be added when the

[Jim Stichnoth, 2015/11/11 17:39:45]

reflow

[sehr, 2015/11/11 22:14:11]

Done.

+      // lea is emitted.
+      Constant *Offset = Ctx->getConstantInt(Ty, 0);

[Jim Stichnoth, 2015/11/11 17:39:45]

John's cool new style:

  Constant *_0 = Ctx->getConstantZero(Ty);

Or:

  constexpr Constant *NoOffset = nullptr;

[sehr, 2015/11/11 22:14:11]

Chose the latter.  Fewer constant lookups is goo.

+      auto *Mem = Traits::X86OperandMem::create(Func, Ty, Var, Offset);
+      _lea(NewVar, Mem);
+      From = NewVar;
+    } else if ((!(Allowed & Legal_Mem) && !MustHaveRegister) ||
+               (RegNum != Variable::NoRegister && RegNum != Var->getRegNum()) ||
+               MustRematerialize) {
       From = copyToReg(From, RegNum);
     }
     return From;