Reland of "MIPS: Optimize load/store with large offset"

src/mips/assembler-mips.cc

Index: src/mips/assembler-mips.cc
diff --git a/src/mips/assembler-mips.cc b/src/mips/assembler-mips.cc
index f5b235d1f6f1f045fe19ea5ef7709cbfa22bbce8..865e64c87d26fabb81a7511d774d1fb9b8440c60 100644
--- a/src/mips/assembler-mips.cc
+++ b/src/mips/assembler-mips.cc
@@ -1784,13 +1784,44 @@ void Assembler::LoadRegPlusOffsetToAt(const MemOperand& src) {
   addu(at, at, src.rm());  // Add base register.
 }
 
+// Helper for base-reg + upper part of offset, when offset is larger than int16.
+// Loads higher part of the offset to AT register.
+// Returns lower part of the offset to be used as offset
+// in Load/Store instructions
+int32_t Assembler::LoadRegPlusUpperOffsetPartToAt(const MemOperand& src) {
+  DCHECK(!src.rm().is(at));
+  int32_t hi = (src.offset_ >> kLuiShift) & kImm16Mask;
+  // If the highest bit of the lower part of the offset is 1, this would make
+  // the offset in the load/store instruction negative. We need to compensate
+  // for this by adding 1 to the upper part of the offset.
+  if (src.offset_ & kNegOffset) {
+    hi += 1;
+  }
+  lui(at, hi);
+  addu(at, at, src.rm());
+  return (src.offset_ & kImm16Mask);
+}
+
+// Helper for loading base-reg + upper offset's part to AT reg when we are using
+// two 32-bit loads/stores instead of one 64-bit
+int32_t Assembler::LoadUpperOffsetForTwoMemoryAccesses(const MemOperand& src) {
+  DCHECK(!src.rm().is(at));
+  if (is_int16((src.offset_ & kImm16Mask) + kIntSize)) {
+    // Only if lower part of offset + kIntSize fits in 16bits
+    return LoadRegPlusUpperOffsetPartToAt(src);
+  }
+  // In case offset's lower part + kIntSize doesn't fit in 16bits,
+  // load reg + hole offset to AT
+  LoadRegPlusOffsetToAt(src);
+  return 0;
+}
 
 void Assembler::lb(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(LB, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(LB, at, rd, 0);  // Equiv to lb(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(LB, at, rd, off16);
   }
 }
 
@@ -1799,8 +1830,8 @@ void Assembler::lbu(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(LBU, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(LBU, at, rd, 0);  // Equiv to lbu(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(LBU, at, rd, off16);
   }
 }
 
@@ -1809,8 +1840,8 @@ void Assembler::lh(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(LH, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(LH, at, rd, 0);  // Equiv to lh(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(LH, at, rd, off16);
   }
 }
 
@@ -1819,8 +1850,8 @@ void Assembler::lhu(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(LHU, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(LHU, at, rd, 0);  // Equiv to lhu(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(LHU, at, rd, off16);
   }
 }
 
@@ -1829,8 +1860,8 @@ void Assembler::lw(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(LW, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(LW, at, rd, 0);  // Equiv to lw(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(LW, at, rd, off16);
   }
 }
 
@@ -1855,8 +1886,8 @@ void Assembler::sb(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(SB, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to store.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(SB, at, rd, 0);  // Equiv to sb(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(SB, at, rd, off16);
   }
 }
 
@@ -1865,8 +1896,8 @@ void Assembler::sh(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(SH, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to store.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(SH, at, rd, 0);  // Equiv to sh(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(SH, at, rd, off16);
   }
 }
 
@@ -1875,8 +1906,8 @@ void Assembler::sw(Register rd, const MemOperand& rs) {
   if (is_int16(rs.offset_)) {
     GenInstrImmediate(SW, rs.rm(), rd, rs.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to store.
-    LoadRegPlusOffsetToAt(rs);
-    GenInstrImmediate(SW, at, rd, 0);  // Equiv to sw(rd, MemOperand(at, 0));
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(rs);
+    GenInstrImmediate(SW, at, rd, off16);
   }
 }
 
@@ -2172,8 +2203,8 @@ void Assembler::lwc1(FPURegister fd, const MemOperand& src) {
   if (is_int16(src.offset_)) {
     GenInstrImmediate(LWC1, src.rm(), fd, src.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
-    LoadRegPlusOffsetToAt(src);
-    GenInstrImmediate(LWC1, at, fd, 0);
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(src);
+    GenInstrImmediate(LWC1, at, fd, off16);
   }
 }
 
@@ -2190,11 +2221,11 @@ void Assembler::ldc1(FPURegister fd, const MemOperand& src) {
       GenInstrImmediate(LWC1, src.rm(), nextfpreg,
                         src.offset_ + Register::kExponentOffset);
     } else {  // Offset > 16 bits, use multiple instructions to load.
-      LoadRegPlusOffsetToAt(src);
-      GenInstrImmediate(LWC1, at, fd, Register::kMantissaOffset);
+      int32_t off16 = LoadUpperOffsetForTwoMemoryAccesses(src);
+      GenInstrImmediate(LWC1, at, fd, off16 + Register::kMantissaOffset);
       FPURegister nextfpreg;
       nextfpreg.setcode(fd.code() + 1);
-      GenInstrImmediate(LWC1, at, nextfpreg, Register::kExponentOffset);
+      GenInstrImmediate(LWC1, at, nextfpreg, off16 + Register::kExponentOffset);
     }
   } else {
     DCHECK(IsFp64Mode() || IsFpxxMode());
@@ -2207,9 +2238,9 @@ void Assembler::ldc1(FPURegister fd, const MemOperand& src) {
                         src.offset_ + Register::kExponentOffset);
       mthc1(at, fd);
     } else {  // Offset > 16 bits, use multiple instructions to load.
-      LoadRegPlusOffsetToAt(src);
-      GenInstrImmediate(LWC1, at, fd, Register::kMantissaOffset);
-      GenInstrImmediate(LW, at, at, Register::kExponentOffset);
+      int32_t off16 = LoadUpperOffsetForTwoMemoryAccesses(src);
+      GenInstrImmediate(LWC1, at, fd, off16 + Register::kMantissaOffset);
+      GenInstrImmediate(LW, at, at, off16 + Register::kExponentOffset);
       mthc1(at, fd);
     }
   }
@@ -2220,8 +2251,8 @@ void Assembler::swc1(FPURegister fd, const MemOperand& src) {
   if (is_int16(src.offset_)) {
     GenInstrImmediate(SWC1, src.rm(), fd, src.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
-    LoadRegPlusOffsetToAt(src);
-    GenInstrImmediate(SWC1, at, fd, 0);
+    int32_t off16 = LoadRegPlusUpperOffsetPartToAt(src);
+    GenInstrImmediate(SWC1, at, fd, off16);
   }
 }
 
@@ -2240,11 +2271,11 @@ void Assembler::sdc1(FPURegister fd, const MemOperand& src) {
       GenInstrImmediate(SWC1, src.rm(), nextfpreg,
                         src.offset_ + Register::kExponentOffset);
     } else {  // Offset > 16 bits, use multiple instructions to load.
-      LoadRegPlusOffsetToAt(src);
-      GenInstrImmediate(SWC1, at, fd, Register::kMantissaOffset);
+      int32_t off16 = LoadUpperOffsetForTwoMemoryAccesses(src);
+      GenInstrImmediate(SWC1, at, fd, off16 + Register::kMantissaOffset);
       FPURegister nextfpreg;
       nextfpreg.setcode(fd.code() + 1);
-      GenInstrImmediate(SWC1, at, nextfpreg, Register::kExponentOffset);
+      GenInstrImmediate(SWC1, at, nextfpreg, off16 + Register::kExponentOffset);
     }
   } else {
     DCHECK(IsFp64Mode() || IsFpxxMode());
@@ -2257,10 +2288,10 @@ void Assembler::sdc1(FPURegister fd, const MemOperand& src) {
       GenInstrImmediate(SW, src.rm(), at,
                         src.offset_ + Register::kExponentOffset);
     } else {  // Offset > 16 bits, use multiple instructions to load.
-      LoadRegPlusOffsetToAt(src);
-      GenInstrImmediate(SWC1, at, fd, Register::kMantissaOffset);
+      int32_t off16 = LoadUpperOffsetForTwoMemoryAccesses(src);
+      GenInstrImmediate(SWC1, at, fd, off16 + Register::kMantissaOffset);
       mfhc1(t8, fd);
-      GenInstrImmediate(SW, at, t8, Register::kExponentOffset);
+      GenInstrImmediate(SW, at, t8, off16 + Register::kExponentOffset);
     }
   }
 }