[ARM, Thumb1] Prevent ARMTargetLowering::isLegalAddressingMode from accepting illegal modes

ARMTargetLowering::isLegalAddressingMode can accept illegal addressing modes
for the Thumb1 target. This causes generation of redundant code and affects
performance.

This fixes PR34106: https://bugs.llvm.org/show_bug.cgi?id=34106

Differential Revision: https://reviews.llvm.org/D36467

llvm-svn: 311649

2 files changed, 22 insertions, 4 deletions

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index 03d0b7e2a74..8d04f59b95c 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -12383,6 +12383,21 @@ bool ARMTargetLowering::isLegalT2ScaledAddressingMode(const AddrMode &AM,
   }
 }
 
+bool ARMTargetLowering::isLegalT1ScaledAddressingMode(const AddrMode &AM,
+                                                      EVT VT) const {
+  const int Scale = AM.Scale;
+
+  // Negative scales are not supported in Thumb1.
+  if (Scale < 0)
+    return false;
+
+  // Thumb1 addressing modes do not support register scaling excepting the
+  // following cases:
+  // 1. Scale == 1 means no scaling.
+  // 2. Scale == 2 this can be lowered to r + r if there is no base register.
+  return (Scale == 1) || (!AM.HasBaseReg && Scale == 2);
+}
+
 /// isLegalAddressingMode - Return true if the addressing mode represented
 /// by AM is legal for this target, for a load/store of the specified type.
 bool ARMTargetLowering::isLegalAddressingMode(const DataLayout &DL,
@@ -12399,10 +12414,6 @@ bool ARMTargetLowering::isLegalAddressingMode(const DataLayout &DL,
   switch (AM.Scale) {
   case 0:  // no scale reg, must be "r+i" or "r", or "i".
     break;
-  case 1:
-    if (Subtarget->isThumb1Only())
-      return false;
-    LLVM_FALLTHROUGH;
   default:
     // ARM doesn't support any R+R*scale+imm addr modes.
     if (AM.BaseOffs)
@@ -12411,6 +12422,9 @@ bool ARMTargetLowering::isLegalAddressingMode(const DataLayout &DL,
     if (!VT.isSimple())
       return false;
 
+    if (Subtarget->isThumb1Only())
+      return isLegalT1ScaledAddressingMode(AM, VT);
+
     if (Subtarget->isThumb2())
       return isLegalT2ScaledAddressingMode(AM, VT);
 
diff --git a/llvm/lib/Target/ARM/ARMISelLowering.h b/llvm/lib/Target/ARM/ARMISelLowering.h
index 7761aa1315e..fd93629f084 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.h
+++ b/llvm/lib/Target/ARM/ARMISelLowering.h
@@ -329,6 +329,10 @@ class InstrItineraryData;
 
     bool isLegalT2ScaledAddressingMode(const AddrMode &AM, EVT VT) const;
 
+    /// \brief Returns true if the addresing mode representing by AM is legal
+    /// for the Thumb1 target, for a load/store of the specified type.
+    bool isLegalT1ScaledAddressingMode(const AddrMode &AM, EVT VT) const;
+
     /// isLegalICmpImmediate - Return true if the specified immediate is legal
     /// icmp immediate, that is the target has icmp instructions which can
     /// compare a register against the immediate without having to materialize