[ARM] Allow truncs as sources in ARM CGP

We previously only allowed truncs as sinks, but now allow them as
sources too. We do this by checking that the result type is the
narrow type that we're trying to optimise for.

Differential Revision: https://reviews.llvm.org/D51978

llvm-svn: 342141

llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp

@@ -175,7 +175,6 @@ static bool generateSignBits(Value *V) {
 /// dealing with icmps but allow any other integer that is <= 16 bits. Void
 /// types are accepted so we can handle switches.
 static bool isSupportedType(Value *V) {
-  LLVM_DEBUG(dbgs() << "ARM CGP: isSupportedType: " << *V << "\n");
   Type *Ty = V->getType();
 
   // Allow voids and pointers, these won't be promoted.
@@ -186,10 +185,8 @@ static bool isSupportedType(Value *V) {
     Ty = cast<PointerType>(Ld->getPointerOperandType())->getElementType();
 
   const IntegerType *IntTy = dyn_cast<IntegerType>(Ty);
-  if (!IntTy) {
-    LLVM_DEBUG(dbgs() << "ARM CGP: No, not an integer.\n");
+  if (!IntTy)
     return false;
-  }
 
   return IntTy->getBitWidth() == ARMCodeGenPrepare::TypeSize;
 }
@@ -204,7 +201,7 @@ static bool isSupportedType(Value *V) {
 static bool isSource(Value *V) {
   if (!isa<IntegerType>(V->getType()))
     return false;
-  // TODO Allow truncs and zext to be sources.
+  // TODO Allow zext to be sources.
   if (isa<Argument>(V))
     return true;
   else if (isa<LoadInst>(V))
@@ -213,6 +210,8 @@ static bool isSource(Value *V) {
     return true;
   else if (auto *Call = dyn_cast<CallInst>(V))
     return Call->hasRetAttr(Attribute::AttrKind::ZExt);
+  else if (auto *Trunc = dyn_cast<TruncInst>(V))
+    return isSupportedType(Trunc);
   return false;
 }
 
@@ -275,10 +274,8 @@ static bool isSafeOverflow(Instruction *I) {
 }
 
 static bool shouldPromote(Value *V) {
-  if (!isa<IntegerType>(V->getType()) || isSink(V)) {
-    LLVM_DEBUG(dbgs() << "ARM CGP: Don't need to promote: " << *V << "\n");
+  if (!isa<IntegerType>(V->getType()) || isSink(V))
     return false;
-  }
 
   if (isSource(V))
     return true;
@@ -358,7 +355,7 @@ void IRPromoter::Mutate(Type *OrigTy,
       Users.push_back(User);
     }
 
-    for (auto &U : Users)
+    for (auto *U : Users)
       U->replaceUsesOfWith(From, To);
   };
 
@@ -502,15 +499,22 @@ void IRPromoter::Mutate(Type *OrigTy,
     }
   }
   LLVM_DEBUG(dbgs() << "ARM CGP: Mutation complete:\n");
+  LLVM_DEBUG(dbgs();
+             for (auto *V : Sources)
+               V->dump();
+             for (auto *I : NewInsts)
+               I->dump();
+             for (auto *V : Visited) {
+               if (!Sources.count(V))
+                 V->dump();
+              });
 }
 
 /// We accept most instructions, as well as Arguments and ConstantInsts. We
 /// Disallow casts other than zext and truncs and only allow calls if their
 /// return value is zeroext. We don't allow opcodes that can introduce sign
 /// bits.
 bool ARMCodeGenPrepare::isSupportedValue(Value *V) {
-  LLVM_DEBUG(dbgs() << "ARM CGP: Is " << *V << " supported?\n");
-
   if (isa<ICmpInst>(V))
     return true;
 
@@ -530,7 +534,11 @@ bool ARMCodeGenPrepare::isSupportedValue(Value *V) {
       isa<LoadInst>(V))
     return isSupportedType(V);
 
-  if (isa<CastInst>(V) && !isa<SExtInst>(V)) 
+  // Truncs can be either sources or sinks.
+  if (auto *Trunc = dyn_cast<TruncInst>(V))
+    return isSupportedType(Trunc) || isSupportedType(Trunc->getOperand(0));
+
+  if (isa<CastInst>(V) && !isa<SExtInst>(V))
     return isSupportedType(cast<CastInst>(V)->getOperand(0));
 
   // Special cases for calls as we need to check for zeroext
@@ -540,10 +548,9 @@ bool ARMCodeGenPrepare::isSupportedValue(Value *V) {
     return isSupportedType(Call) &&
            Call->hasRetAttr(Attribute::AttrKind::ZExt);
 
-  if (!isa<BinaryOperator>(V)) {
-    LLVM_DEBUG(dbgs() << "ARM CGP: No, not a binary operator.\n");
+  if (!isa<BinaryOperator>(V))
     return false;
-  }
+
   if (!isSupportedType(V))
     return false;
 
@@ -645,10 +652,8 @@ bool ARMCodeGenPrepare::TryToPromote(Value *V) {
     // the tree has already been explored.
     // TODO: This could limit the transform, ie if we try to promote something
     // from an i8 and fail first, before trying an i16.
-    if (AllVisited.count(V)) {
-      LLVM_DEBUG(dbgs() << "ARM CGP: Already visited this: " << *V << "\n");
+    if (AllVisited.count(V))
       return false;
-    }
 
     CurrentVisited.insert(V);
     AllVisited.insert(V);
@@ -728,7 +733,6 @@ bool ARMCodeGenPrepare::runOnFunction(Function &F) {
         if (CI.isSigned() || !isa<IntegerType>(CI.getOperand(0)->getType()))
           continue;
 
-        LLVM_DEBUG(dbgs() << "ARM CGP: Searching from: " << CI << "\n");
         for (auto &Op : CI.operands()) {
           if (auto *I = dyn_cast<Instruction>(Op))
             MadeChange |= TryToPromote(I);

llvm/test/CodeGen/ARM/arm-cgp-casts.ll

@@ -190,7 +190,6 @@ exit:
 ; CHECK-COMMON-LABEL: phi_feeding_switch
 ; CHECK-COMMON: ldrb
 ; CHECK-COMMON: uxtb
-; CHECK-COMMON: uxtb
 define void @phi_feeding_switch(i8* %memblock, i8* %store, i16 %arg) {
 entry:
   %pre = load i8, i8* %memblock, align 1