Add the ability to use GEPs for address sinking in CGP

The current memory-instruction optimization logic in CGP, which sinks parts of
the address computation that can be adsorbed by the addressing mode, does this
by explicitly converting the relevant part of the address computation into
IR-level integer operations (making use of ptrtoint and inttoptr). For most
targets this is currently not a problem, but for targets wishing to make use of
IR-level aliasing analysis during CodeGen, the use of ptrtoint/inttoptr is a
problem for two reasons:
  1. BasicAA becomes less powerful in the face of the ptrtoint/inttoptr
  2. In cases where type-punning was used, and BasicAA was used
     to override TBAA, BasicAA may no longer do so. (this had forced us to disable
     all use of TBAA in CodeGen; something which we can now enable again)

This (use of GEPs instead of ptrtoint/inttoptr) is not currently enabled by
default (except for those targets that use AA during CodeGen), and so aside
from some PowerPC subtargets and SystemZ, there should be no change in
behavior. We may be able to switch completely away from the ptrtoint/inttoptr
sinking on all targets, but further testing is required.

I've doubled-up on a number of existing tests that are sensitive to the
address sinking behavior (including some store-merging tests that are
sensitive to the order of the resulting ADD operations at the SDAG level).

llvm-svn: 206092

1 files changed, 126 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index 9765485b5d5..91d702a5660 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -39,6 +39,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetLibraryInfo.h"
 #include "llvm/Target/TargetLowering.h"
+#include "llvm/Target/TargetSubtargetInfo.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/BuildLibCalls.h"
 #include "llvm/Transforms/Utils/BypassSlowDivision.h"
@@ -70,6 +71,10 @@ static cl::opt<bool> DisableSelectToBranch(
   "disable-cgp-select2branch", cl::Hidden, cl::init(false),
   cl::desc("Disable select to branch conversion."));
 
+static cl::opt<bool> AddrSinkUsingGEPs(
+  "addr-sink-using-gep", cl::Hidden, cl::init(false),
+  cl::desc("Address sinking in CGP using GEPs."));
+
 static cl::opt<bool> EnableAndCmpSinking(
    "enable-andcmp-sinking", cl::Hidden, cl::init(true),
    cl::desc("Enable sinkinig and/cmp into branches."));
@@ -2423,6 +2428,127 @@ bool CodeGenPrepare::OptimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
                  << *MemoryInst);
     if (SunkAddr->getType() != Addr->getType())
       SunkAddr = Builder.CreateBitCast(SunkAddr, Addr->getType());
+  } else if (AddrSinkUsingGEPs || (!AddrSinkUsingGEPs.getNumOccurrences() &&
+               TM && TM->getSubtarget<TargetSubtargetInfo>().useAA())) {
+    // By default, we use the GEP-based method when AA is used later. This
+    // prevents new inttoptr/ptrtoint pairs from degrading AA capabilities.
+    DEBUG(dbgs() << "CGP: SINKING nonlocal addrmode: " << AddrMode << " for "
+                 << *MemoryInst);
+    Type *IntPtrTy = TLI->getDataLayout()->getIntPtrType(Addr->getType());
+    Value *ResultPtr = 0, *ResultIndex = 0;
+
+    // First, find the pointer.
+    if (AddrMode.BaseReg && AddrMode.BaseReg->getType()->isPointerTy()) {
+      ResultPtr = AddrMode.BaseReg;
+      AddrMode.BaseReg = 0;
+    }
+
+    if (AddrMode.Scale && AddrMode.ScaledReg->getType()->isPointerTy()) {
+      // We can't add more than one pointer together, nor can we scale a
+      // pointer (both of which seem meaningless).
+      if (ResultPtr || AddrMode.Scale != 1)
+        return false;
+
+      ResultPtr = AddrMode.ScaledReg;
+      AddrMode.Scale = 0;
+    }
+
+    if (AddrMode.BaseGV) {
+      if (ResultPtr)
+        return false;
+
+      ResultPtr = AddrMode.BaseGV;
+    }
+
+    // If the real base value actually came from an inttoptr, then the matcher
+    // will look through it and provide only the integer value. In that case,
+    // use it here.
+    if (!ResultPtr && AddrMode.BaseReg) {
+      ResultPtr =
+        Builder.CreateIntToPtr(AddrMode.BaseReg, Addr->getType(), "sunkaddr");
+      AddrMode.BaseReg = 0;
+    } else if (!ResultPtr && AddrMode.Scale == 1) {
+      ResultPtr =
+        Builder.CreateIntToPtr(AddrMode.ScaledReg, Addr->getType(), "sunkaddr");
+      AddrMode.Scale = 0;
+    }
+
+    if (!ResultPtr &&
+        !AddrMode.BaseReg && !AddrMode.Scale && !AddrMode.BaseOffs) {
+      SunkAddr = Constant::getNullValue(Addr->getType());
+    } else if (!ResultPtr) {
+      return false;
+    } else {
+      Type *I8PtrTy =
+        Builder.getInt8PtrTy(Addr->getType()->getPointerAddressSpace());
+
+      // Start with the base register. Do this first so that subsequent address
+      // matching finds it last, which will prevent it from trying to match it
+      // as the scaled value in case it happens to be a mul. That would be
+      // problematic if we've sunk a different mul for the scale, because then
+      // we'd end up sinking both muls.
+      if (AddrMode.BaseReg) {
+        Value *V = AddrMode.BaseReg;
+        if (V->getType() != IntPtrTy)
+          V = Builder.CreateIntCast(V, IntPtrTy, /*isSigned=*/true, "sunkaddr");
+
+        ResultIndex = V;
+      }
+
+      // Add the scale value.
+      if (AddrMode.Scale) {
+        Value *V = AddrMode.ScaledReg;
+        if (V->getType() == IntPtrTy) {
+          // done.
+        } else if (cast<IntegerType>(IntPtrTy)->getBitWidth() <
+                   cast<IntegerType>(V->getType())->getBitWidth()) {
+          V = Builder.CreateTrunc(V, IntPtrTy, "sunkaddr");
+        } else {
+          // It is only safe to sign extend the BaseReg if we know that the math
+          // required to create it did not overflow before we extend it. Since
+          // the original IR value was tossed in favor of a constant back when
+          // the AddrMode was created we need to bail out gracefully if widths
+          // do not match instead of extending it.
+          Instruction *I = dyn_cast_or_null<Instruction>(ResultIndex);
+          if (I && (ResultIndex != AddrMode.BaseReg))
+            I->eraseFromParent();
+          return false;
+        }
+
+        if (AddrMode.Scale != 1)
+          V = Builder.CreateMul(V, ConstantInt::get(IntPtrTy, AddrMode.Scale),
+                                "sunkaddr");
+        if (ResultIndex)
+          ResultIndex = Builder.CreateAdd(ResultIndex, V, "sunkaddr");
+        else
+          ResultIndex = V;
+      }
+
+      // Add in the Base Offset if present.
+      if (AddrMode.BaseOffs) {
+        Value *V = ConstantInt::get(IntPtrTy, AddrMode.BaseOffs);
+        if (ResultIndex) {
+	  // We need to add this separately from the scale above to help with
+	  // SDAG consecutive load/store merging.
+          if (ResultPtr->getType() != I8PtrTy)
+            ResultPtr = Builder.CreateBitCast(ResultPtr, I8PtrTy);
+          ResultPtr = Builder.CreateGEP(ResultPtr, ResultIndex, "sunkaddr");
+        }
+
+        ResultIndex = V;
+      }
+
+      if (!ResultIndex) {
+        SunkAddr = ResultPtr;
+      } else {
+        if (ResultPtr->getType() != I8PtrTy)
+          ResultPtr = Builder.CreateBitCast(ResultPtr, I8PtrTy);
+        SunkAddr = Builder.CreateGEP(ResultPtr, ResultIndex, "sunkaddr");
+      }
+
+      if (SunkAddr->getType() != Addr->getType())
+        SunkAddr = Builder.CreateBitCast(SunkAddr, Addr->getType());
+    }
   } else {
     DEBUG(dbgs() << "CGP: SINKING nonlocal addrmode: " << AddrMode << " for "
                  << *MemoryInst);