Update fake-splitting implementation on ARM64

To facilitate generating unwind info, fake-splitting now places the
read-only data section after the cold section. This allows the
hot/cold code sections to be truly contiguous.

Author: Aman Khalid

src/coreclr/jit/compiler.h

@@ -7646,7 +7646,7 @@ class Compiler
 
     // ICorJitInfo wrappers
 
-    void eeAllocMem(AllocMemArgs* args);
+    void eeAllocMem(AllocMemArgs* args, const UNATIVE_OFFSET roDataSectionAlignment);
 
     void eeReserveUnwindInfo(bool isFunclet, bool isColdCode, ULONG unwindSize);
 

src/coreclr/jit/ee_il_dll.cpp

@@ -1122,34 +1122,64 @@ void Compiler::eeDispLineInfos()
  * (e.g., host AMD64, target ARM64), then VM will get confused anyway.
  */
 
-void Compiler::eeAllocMem(AllocMemArgs* args)
+void Compiler::eeAllocMem(AllocMemArgs* args, const UNATIVE_OFFSET roDataSectionAlignment)
 {
 #ifdef DEBUG
-    const UNATIVE_OFFSET hotSizeRequest  = args->hotCodeSize;
-    const UNATIVE_OFFSET coldSizeRequest = args->coldCodeSize;
 
-    // Fake splitting implementation: place hot/cold code in contiguous section
-    if (JitConfig.JitFakeProcedureSplitting() && (coldSizeRequest > 0))
+    // Fake splitting implementation: place hot/cold code in contiguous section.
+    UNATIVE_OFFSET coldCodeOffset = 0;
+    if (JitConfig.JitFakeProcedureSplitting() && (args->coldCodeSize > 0))
     {
-        args->hotCodeSize  = hotSizeRequest + coldSizeRequest;
+        coldCodeOffset = args->hotCodeSize;
+        assert(coldCodeOffset > 0);
+        args->hotCodeSize += args->coldCodeSize;
         args->coldCodeSize = 0;
     }
-#endif
+
+#endif // DEBUG
+
+#if defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64)
+
+    // For arm64/LoongArch64, we want to allocate JIT data always adjacent to code similar to what native compiler does.
+    // This way allows us to use a single `ldr` to access such data like float constant/jmp table.
+    // For LoongArch64 using `pcaddi + ld` to access such data.
+
+    UNATIVE_OFFSET roDataAlignmentDelta = 0;
+    if (args->roDataSize > 0)
+    {
+        roDataAlignmentDelta = AlignmentPad(args->hotCodeSize, roDataSectionAlignment);
+    }
+
+    const UNATIVE_OFFSET roDataOffset = args->hotCodeSize + roDataAlignmentDelta;
+    args->hotCodeSize                 = roDataOffset + args->roDataSize;
+    args->roDataSize                  = 0;
+
+#endif // defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64)
 
     info.compCompHnd->allocMem(args);
 
 #ifdef DEBUG
-    if (JitConfig.JitFakeProcedureSplitting() && (coldSizeRequest > 0))
-    {
-        // Fix up hot/cold code pointers
-        args->coldCodeBlock   = ((BYTE*)args->hotCodeBlock) + hotSizeRequest;
-        args->coldCodeBlockRW = ((BYTE*)args->hotCodeBlockRW) + hotSizeRequest;
 
-        // Reset args' hot/cold code sizes in case caller reads them later
-        args->hotCodeSize  = hotSizeRequest;
-        args->coldCodeSize = coldSizeRequest;
+    if (JitConfig.JitFakeProcedureSplitting() && (coldCodeOffset > 0))
+    {
+        // Fix up cold code pointers. Cold section is adjacent to hot section.
+        assert(args->coldCodeBlock == nullptr);
+        assert(args->coldCodeBlockRW == nullptr);
+        args->coldCodeBlock   = ((BYTE*)args->hotCodeBlock) + coldCodeOffset;
+        args->coldCodeBlockRW = ((BYTE*)args->hotCodeBlockRW) + coldCodeOffset;
     }
-#endif
+
+#endif // DEBUG
+
+#if defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64)
+
+    // Fix up data section pointers.
+    assert(args->roDataBlock == nullptr);
+    assert(args->roDataBlockRW == nullptr);
+    args->roDataBlock   = ((BYTE*)args->hotCodeBlock) + roDataOffset;
+    args->roDataBlockRW = ((BYTE*)args->hotCodeBlockRW) + roDataOffset;
+
+#endif // defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64)
 }
 
 void Compiler::eeReserveUnwindInfo(bool isFunclet, bool isColdCode, ULONG unwindSize)

src/coreclr/jit/emit.cpp

@@ -6304,38 +6304,13 @@ unsigned emitter::emitEndCodeGen(Compiler* comp,
     AllocMemArgs args;
     memset(&args, 0, sizeof(args));
 
-#if defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64)
-    // For arm64/LoongArch64, we want to allocate JIT data always adjacent to code similar to what native compiler does.
-    // This way allows us to use a single `ldr` to access such data like float constant/jmp table.
-
-    const UNATIVE_OFFSET roDataAlignmentDelta =
-        (UNATIVE_OFFSET)ALIGN_UP(emitTotalHotCodeSize, emitConsDsc.alignment) - emitTotalHotCodeSize;
-
-    args.hotCodeSize  = emitTotalHotCodeSize + roDataAlignmentDelta + emitConsDsc.dsdOffs;
-    args.coldCodeSize = emitTotalColdCodeSize;
-    args.roDataSize   = 0;
-    args.xcptnsCount  = xcptnsCount;
-    args.flag         = allocMemFlag;
-
-    emitComp->eeAllocMem(&args);
-
-    codeBlock       = (BYTE*)args.hotCodeBlock;
-    codeBlockRW     = (BYTE*)args.hotCodeBlockRW;
-    coldCodeBlock   = (BYTE*)args.coldCodeBlock;
-    coldCodeBlockRW = (BYTE*)args.coldCodeBlockRW;
-
-    consBlock   = codeBlock + emitTotalHotCodeSize + roDataAlignmentDelta;
-    consBlockRW = codeBlockRW + emitTotalHotCodeSize + roDataAlignmentDelta;
-
-#else
-
     args.hotCodeSize  = emitTotalHotCodeSize;
     args.coldCodeSize = emitTotalColdCodeSize;
     args.roDataSize   = emitConsDsc.dsdOffs;
     args.xcptnsCount  = xcptnsCount;
     args.flag         = allocMemFlag;
 
-    emitComp->eeAllocMem(&args);
+    emitComp->eeAllocMem(&args, emitConsDsc.alignment);
 
     codeBlock       = (BYTE*)args.hotCodeBlock;
     codeBlockRW     = (BYTE*)args.hotCodeBlockRW;
@@ -6344,8 +6319,6 @@ unsigned emitter::emitEndCodeGen(Compiler* comp,
     consBlock       = (BYTE*)args.roDataBlock;
     consBlockRW     = (BYTE*)args.roDataBlockRW;
 
-#endif
-
 #ifdef DEBUG
     if ((allocMemFlag & CORJIT_ALLOCMEM_FLG_32BYTE_ALIGN) != 0)
     {

src/coreclr/jit/emitarm64.cpp

@@ -8437,8 +8437,7 @@ void emitter::emitIns_J(instruction ins, BasicBlock* dst, int instrCount)
     {
         case INS_bl_local:
             idjShort = true;
-            fmt = IF_BI_0A;
-            break;
+            FALLTHROUGH;
         case INS_b:
             // Unconditional jump is a single form.
             // Assume is long in case we cross hot/cold sections.
@@ -9841,9 +9840,6 @@ BYTE* emitter::emitOutputLJ(insGroup* ig, BYTE* dst, instrDesc* i)
                 // Special case: emit add + ld1 instructions for loading 16-byte data into vector register.
                 if (isVectorRegister(dstReg) && (opSize == EA_16BYTE))
                 {
-                    // Low 4 bits should be 0 -- 16-byte JIT data should be aligned on 16 bytes.
-                    assert((imm12 & 15) == 0);
-
                     const emitAttr elemSize = EA_1BYTE;
                     const insOpts  opt      = optMakeArrangement(opSize, elemSize);