[PATCH] D135894: [clang][RISCV] Set vscale_range attribute based on presence of "v" extension

[Philip Reames via Phabricator via llvm-commits]

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This follows the path that AArch64 SVE has taken.  Doing this via a function attribute set in the frontend is basically a workaround for the fact that several analyzes which need the information (i.e. known bits, lvi, scev) can't easily use TTI without significant amounts of plumbing changes.

This patch hard codes "v" numbers, and directly follows the SVE precedent as a result.  In a follow up, I hope to drive this from RISCVISAInfo.h/cpp instead, but the MinVLen number being returned from that interface seemed to always be 0 (which is wrong), and I haven't figured out what's going wrong there.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D135894

Files:
  clang/lib/Basic/Targets/RISCV.cpp
  clang/lib/Basic/Targets/RISCV.h
  clang/test/CodeGen/riscv-vector-bits-vscale-range.c


Index: clang/test/CodeGen/riscv-vector-bits-vscale-range.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/riscv-vector-bits-vscale-range.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=1 -mvscale-max=1 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=1
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=2 -mvscale-max=2 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=2
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=4 -mvscale-max=4 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=4
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=8 -mvscale-max=8 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=8
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=16 -mvscale-max=16 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=16
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=1 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=1 --check-prefix=CHECK-NOMAX
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=2 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=2 --check-prefix=CHECK-NOMAX
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=4 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=4 --check-prefix=CHECK-NOMAX
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=8 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=8 --check-prefix=CHECK-NOMAX
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=16 -S -emit-llvm -o - %s | FileCheck %s -D#VBITS=16 --check-prefix=CHECK-NOMAX
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -mvscale-min=1 -mvscale-max=0 -S -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-UNBOUNDED
+// RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -S -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-NONE
+
+// CHECK-LABEL: @func() #0
+// CHECK: attributes #0 = { {{.*}} vscale_range([[#VBITS]],[[#VBITS]]) {{.*}} }
+// CHECK-NOMAX: attributes #0 = { {{.*}} vscale_range([[#VBITS]],0) {{.*}} }
+// CHECK-UNBOUNDED: attributes #0 = { {{.*}} vscale_range(1,0) {{.*}} }
+// CHECK-NONE: attributes #0 = { {{.*}} vscale_range(2,1024) {{.*}} }
+void func(void) {}
Index: clang/lib/Basic/Targets/RISCV.h
===================================================================
--- clang/lib/Basic/Targets/RISCV.h
+++ clang/lib/Basic/Targets/RISCV.h
@@ -90,6 +90,9 @@
                  StringRef CPU,
                  const std::vector<std::string> &FeaturesVec) const override;
 
+  Optional<std::pair<unsigned, unsigned>>
+  getVScaleRange(const LangOptions &LangOpts) const override;
+
   bool hasFeature(StringRef Feature) const override;
 
   bool handleTargetFeatures(std::vector<std::string> &Features,
Index: clang/lib/Basic/Targets/RISCV.cpp
===================================================================
--- clang/lib/Basic/Targets/RISCV.cpp
+++ clang/lib/Basic/Targets/RISCV.cpp
@@ -246,6 +246,19 @@
   return TargetInfo::initFeatureMap(Features, Diags, CPU, ImpliedFeatures);
 }
 
+Optional<std::pair<unsigned, unsigned>>
+RISCVTargetInfo::getVScaleRange(const LangOptions &LangOpts) const {
+  if (LangOpts.VScaleMin || LangOpts.VScaleMax)
+    return std::pair<unsigned, unsigned>(
+        LangOpts.VScaleMin ? LangOpts.VScaleMin : 1, LangOpts.VScaleMax);
+
+  if (hasFeature("v"))
+    // Minium VLEN=128, Maximum VLEN=64k, and RISCV::RVVBitsPerBlock is 64.
+    return std::pair<unsigned, unsigned>(2, 1024);
+
+  return None;
+}
+
 /// Return true if has this feature, need to sync with handleTargetFeatures.
 bool RISCVTargetInfo::hasFeature(StringRef Feature) const {
   bool Is64Bit = getTriple().getArch() == llvm::Triple::riscv64;


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