Bump X86 Darwin MaxVectorAlign to 64, for AVX512.

[ab]

Summary

Without this, 64-byte vector types (__m512), specified to be 64-byte aligned in the AVX512 draft SysV ABI, will only be 32-byte aligned.

One might raise a couple valid concerns:

• this doesn't change alignment of anything other than clang-generated vector code. So malloc() and all will still only be 16-byte aligned.
• we've gotten to a point where unaligned accesses are good enough, why care about alignment?

To which I pedantically counter:

• there's precedent: AVX bumped alignment to 32, so vector users are already familiar with the issue.
• because the spec says so ;)

[rjmccall]

Should we conditionalize this on whether AVX (for 32-byte) and AVX-512 (for 64-byte) are enabled? I'm willing to accept that we shouldn't; just want to hear your thoughts.

[ab]

In D10724#194990, @rjmccall wrote:

Should we conditionalize this on whether AVX (for 32-byte) and AVX-512 (for 64-byte) are enabled? I'm willing to accept that we shouldn't; just want to hear your thoughts.

I think that would make sense.

I thought I saw a justification for unconditionally using 256 in the original AVX patch, but now that I look again I don't think there is one, and I can't think of one.

[rjmccall]

Okay. Go ahead and send a patch to do that, then, please.

cfe/trunk/lib/Basic/Targets.cpp

DarwinI386TargetInfo(const llvm::Triple &Triple)
     HasAlignMac68kSupport = true;
   }
 
   bool handleTargetFeatures(std::vector<std::string> &Features,
                             DiagnosticsEngine &Diags) override {
     if (!DarwinTargetInfo<X86_32TargetInfo>::handleTargetFeatures(Features,
                                                                   Diags))
       return false;
-    // Now that we know if we have AVX, we can decide how to align vectors.
-    MaxVectorAlign = hasFeature("avx") ? 256 : 128;
+    // We now know the features we have: we can decide how to align vectors.
+    MaxVectorAlign =
+        hasFeature("avx512f") ? 512 : hasFeature("avx") ? 256 : 128;
     return true;
   }
 };
 
 // x86-32 Windows target
 class WindowsX86_32TargetInfo : public WindowsTargetInfo<X86_32TargetInfo> {
 public:
   WindowsX86_32TargetInfo(const llvm::Triple &Triple)
DarwinX86_64TargetInfo(const llvm::Triple &Triple)
     DataLayoutString = "e-m:o-i64:64-f80:128-n8:16:32:64-S128";
   }
 
   bool handleTargetFeatures(std::vector<std::string> &Features,
                             DiagnosticsEngine &Diags) override {
     if (!DarwinTargetInfo<X86_64TargetInfo>::handleTargetFeatures(Features,
                                                                   Diags))
       return false;
-    // Now that we know if we have AVX, we can decide how to align vectors.
-    MaxVectorAlign = hasFeature("avx") ? 256 : 128;
+    // We now know the features we have: we can decide how to align vectors.
+    MaxVectorAlign =
+        hasFeature("avx512f") ? 512 : hasFeature("avx") ? 256 : 128;
     return true;
   }
 };
 
 class OpenBSDX86_64TargetInfo : public OpenBSDTargetInfo<X86_64TargetInfo> {
 public:
   OpenBSDX86_64TargetInfo(const llvm::Triple &Triple)
       : OpenBSDTargetInfo<X86_64TargetInfo>(Triple) {

cfe/trunk/test/CodeGen/vector-alignment.c

 // RUN: %clang_cc1 -w -triple x86_64-apple-darwin10 \
 // RUN:  -emit-llvm -o - %s | FileCheck %s --check-prefix=ALL --check-prefix=SSE
 // RUN: %clang_cc1 -w -triple   i386-apple-darwin10 \
 // RUN:  -emit-llvm -o - %s | FileCheck %s --check-prefix=ALL --check-prefix=SSE
 // RUN: %clang_cc1 -w -triple x86_64-apple-darwin10 -target-feature +avx \
 // RUN:  -emit-llvm -o - %s | FileCheck %s --check-prefix=ALL --check-prefix=AVX
 // RUN: %clang_cc1 -w -triple   i386-apple-darwin10 -target-feature +avx \
 // RUN:  -emit-llvm -o - %s | FileCheck %s --check-prefix=ALL --check-prefix=AVX
+// RUN: %clang_cc1 -w -triple x86_64-apple-darwin10 -target-feature +avx512f \
+// RUN:  -emit-llvm -o - %s | FileCheck %s --check-prefix=ALL --check-prefix=AVX512
+// RUN: %clang_cc1 -w -triple   i386-apple-darwin10 -target-feature +avx512f \
+// RUN:  -emit-llvm -o - %s | FileCheck %s --check-prefix=ALL --check-prefix=AVX512
 // rdar://11759609
 
 // At or below target max alignment with no aligned attribute should align based
 // on the size of vector.
 double __attribute__((vector_size(16))) v1;
 // SSE: @v1 {{.*}}, align 16
 // AVX: @v1 {{.*}}, align 16
+// AVX512: @v1 {{.*}}, align 16
 double __attribute__((vector_size(32))) v2;
 // SSE: @v2 {{.*}}, align 16
 // AVX: @v2 {{.*}}, align 32
+// AVX512: @v2 {{.*}}, align 32
 
 // Alignment above target max alignment with no aligned attribute should align
 // based on the target max.
 double __attribute__((vector_size(64))) v3;
 // SSE: @v3 {{.*}}, align 16
 // AVX: @v3 {{.*}}, align 32
+// AVX512: @v3 {{.*}}, align 64
 double __attribute__((vector_size(1024))) v4;
 // SSE: @v4 {{.*}}, align 16
 // AVX: @v4 {{.*}}, align 32
+// AVX512: @v4 {{.*}}, align 64
 
 // Aliged attribute should always override.
 double __attribute__((vector_size(16), aligned(16))) v5;
 // ALL: @v5 {{.*}}, align 16
 double __attribute__((vector_size(16), aligned(64))) v6;
 // ALL: @v6 {{.*}}, align 64
 double __attribute__((vector_size(32), aligned(16))) v7;
 // ALL: @v7 {{.*}}, align 16
 double __attribute__((vector_size(32), aligned(64))) v8;
 // ALL: @v8 {{.*}}, align 64
 
 // Check non-power of 2 widths.
 double __attribute__((vector_size(24))) v9;
 // SSE: @v9 {{.*}}, align 16
 // AVX: @v9 {{.*}}, align 32
+// AVX512: @v9 {{.*}}, align 32
 double __attribute__((vector_size(40))) v10;
 // SSE: @v10 {{.*}}, align 16
 // AVX: @v10 {{.*}}, align 32
+// AVX512: @v10 {{.*}}, align 64
 
 // Check non-power of 2 widths with aligned attribute.
 double __attribute__((vector_size(24), aligned(64))) v11;
 // ALL: @v11 {{.*}}, align 64
 double __attribute__((vector_size(80), aligned(16))) v12;
 // ALL: @v12 {{.*}}, align 16