Add a natural stack alignment field to TargetData, and prevent InstCombine from

promoting allocas to preferred alignments that exceed the natural
alignment. This avoids some potentially expensive dynamic stack realignments.

The natural stack alignment is set in target data strings via the "S<size>"
option. Size is in bits and must be a multiple of 8. The natural stack alignment
defaults to "unspecified" (represented by a zero value), and the "unspecified"
value does not prevent any alignment promotions. Target maintainers that care
about avoiding promotions should explicitly add the "S<size>" option to their
target data strings.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141599 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 27 insertions, 12 deletions

diff --git a/lib/Target/ARM/ARMTargetMachine.cpp b/lib/Target/ARM/ARMTargetMachine.cpp
index f779ede3e3..96b1e89b0d 100644
--- a/lib/Target/ARM/ARMTargetMachine.cpp
+++ b/lib/Target/ARM/ARMTargetMachine.cpp
@@ -53,9 +53,12 @@ ARMTargetMachine::ARMTargetMachine(const Target &T, StringRef TT,
   : ARMBaseTargetMachine(T, TT, CPU, FS, RM, CM), InstrInfo(Subtarget),
     DataLayout(Subtarget.isAPCS_ABI() ?
                std::string("e-p:32:32-f64:32:64-i64:32:64-"
-                           "v128:32:128-v64:32:64-n32") :
+                           "v128:32:128-v64:32:64-n32-S32") :
+               Subtarget.isAAPCS_ABI() ?
                std::string("e-p:32:32-f64:64:64-i64:64:64-"
-                           "v128:64:128-v64:64:64-n32")),
+                           "v128:64:128-v64:64:64-n32-S64") :
+               std::string("e-p:32:32-f64:64:64-i64:64:64-"
+                           "v128:64:128-v64:64:64-n32-S32")),
     ELFWriterInfo(*this),
     TLInfo(*this),
     TSInfo(*this),
@@ -75,10 +78,14 @@ ThumbTargetMachine::ThumbTargetMachine(const Target &T, StringRef TT,
     DataLayout(Subtarget.isAPCS_ABI() ?
                std::string("e-p:32:32-f64:32:64-i64:32:64-"
                            "i16:16:32-i8:8:32-i1:8:32-"
-                           "v128:32:128-v64:32:64-a:0:32-n32") :
+                           "v128:32:128-v64:32:64-a:0:32-n32-S32") :
+               Subtarget.isAAPCS_ABI() ?
+               std::string("e-p:32:32-f64:64:64-i64:64:64-"
+                           "i16:16:32-i8:8:32-i1:8:32-"
+                           "v128:64:128-v64:64:64-a:0:32-n32-S64") :
                std::string("e-p:32:32-f64:64:64-i64:64:64-"
                            "i16:16:32-i8:8:32-i1:8:32-"
-                           "v128:64:128-v64:64:64-a:0:32-n32")),
+                           "v128:64:128-v64:64:64-a:0:32-n32-S32")),
     ELFWriterInfo(*this),
     TLInfo(*this),
     TSInfo(*this),
diff --git a/lib/Target/TargetData.cpp b/lib/Target/TargetData.cpp
index 1dfd9a83da..bd6a6b67be 100644
--- a/lib/Target/TargetData.cpp
+++ b/lib/Target/TargetData.cpp
@@ -139,6 +139,7 @@ void TargetData::init(StringRef Desc) {
   PointerMemSize = 8;
   PointerABIAlign = 8;
   PointerPrefAlign = PointerABIAlign;
+  StackNaturalAlign = 0;
 
   // Default alignments
   setAlignment(INTEGER_ALIGN,   1,  1, 1);   // i1
@@ -218,7 +219,12 @@ void TargetData::init(StringRef Desc) {
         Token = Split.second;
       } while (!Specifier.empty() || !Token.empty());
       break;
-
+    case 'S': // Stack natural alignment.
+      StackNaturalAlign = getInt(Specifier.substr(1));
+      StackNaturalAlign /= 8;
+      // FIXME: Should we really be truncating these alingments and
+      // sizes silently?
+      break;
     default:
       break;
     }
@@ -372,7 +378,9 @@ std::string TargetData::getStringRepresentation() const {
 
   OS << (LittleEndian ? "e" : "E")
      << "-p:" << PointerMemSize*8 << ':' << PointerABIAlign*8
-     << ':' << PointerPrefAlign*8;
+     << ':' << PointerPrefAlign*8
+     << "-S" << StackNaturalAlign*8;
+
   for (unsigned i = 0, e = Alignments.size(); i != e; ++i) {
     const TargetAlignElem &AI = Alignments[i];
     OS << '-' << (char)AI.AlignType << AI.TypeBitWidth << ':'
diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt
index f16ec029e9..7d901afae4 100644
--- a/lib/Target/X86/README-SSE.txt
+++ b/lib/Target/X86/README-SSE.txt
@@ -862,7 +862,7 @@ define float @bar(float %x) nounwind {
 
 This IR (from PR6194):
 
-target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-darwin10.0.0"
 
 %0 = type { double, double }
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index b98f5fbb99..b407955060 100644
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -1217,7 +1217,7 @@ Also check why xmm7 is not used at all in the function.
 
 Take the following:
 
-target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-S128"
 target triple = "i386-apple-darwin8"
 @in_exit.4870.b = internal global i1 false		; <i1*> [#uses=2]
 define fastcc void @abort_gzip() noreturn nounwind  {
diff --git a/lib/Target/X86/X86TargetMachine.cpp b/lib/Target/X86/X86TargetMachine.cpp
index 683d6aa0dd..1dcad35c2e 100644
--- a/lib/Target/X86/X86TargetMachine.cpp
+++ b/lib/Target/X86/X86TargetMachine.cpp
@@ -34,11 +34,11 @@ X86_32TargetMachine::X86_32TargetMachine(const Target &T, StringRef TT,
                                          Reloc::Model RM, CodeModel::Model CM)
   : X86TargetMachine(T, TT, CPU, FS, RM, CM, false),
     DataLayout(getSubtargetImpl()->isTargetDarwin() ?
-               "e-p:32:32-f64:32:64-i64:32:64-f80:128:128-f128:128:128-n8:16:32" :
+               "e-p:32:32-f64:32:64-i64:32:64-f80:128:128-f128:128:128-n8:16:32-S128" :
                (getSubtargetImpl()->isTargetCygMing() ||
                 getSubtargetImpl()->isTargetWindows()) ?
-               "e-p:32:32-f64:64:64-i64:64:64-f80:32:32-f128:128:128-n8:16:32" :
-               "e-p:32:32-f64:32:64-i64:32:64-f80:32:32-f128:128:128-n8:16:32"),
+               "e-p:32:32-f64:64:64-i64:64:64-f80:32:32-f128:128:128-n8:16:32-S32" :
+               "e-p:32:32-f64:32:64-i64:32:64-f80:32:32-f128:128:128-n8:16:32-S32"),
     InstrInfo(*this),
     TSInfo(*this),
     TLInfo(*this),
@@ -50,7 +50,7 @@ X86_64TargetMachine::X86_64TargetMachine(const Target &T, StringRef TT,
                                          StringRef CPU, StringRef FS,
                                          Reloc::Model RM, CodeModel::Model CM)
   : X86TargetMachine(T, TT, CPU, FS, RM, CM, true),
-    DataLayout("e-p:64:64-s:64-f64:64:64-i64:64:64-f80:128:128-f128:128:128-n8:16:32:64"),
+    DataLayout("e-p:64:64-s:64-f64:64:64-i64:64:64-f80:128:128-f128:128:128-n8:16:32:64-S128"),
     InstrInfo(*this),
     TSInfo(*this),
     TLInfo(*this),