[RISCV] Use Zvl*b as a lower bound for VScaleRange.

[craig.topper]

Summary

The backend has a fatal error in RISCVSubtarget::getMinRVVVectorSizeInBits
if RVVVectorBitsMin is less than the Zvl length from -march. Now
RVVVectorBitsMin is connected to VScaleRange in the backend, we
can trip this fatal error.

This patch adds the Zvl*b length as a lower bound to protect this.
The test is updated to test vscale-min with Zvl64b instead of V.

I'd like to do a proper diagnostic for this, but I don't think we
can do that from this function. Since -mvscale-min is an internal cc1
option, I'm not sure it's a big deal.

I'm planning to add a driver option -msve-vector-bits. I will
probably implement a diagnostic for that.

[kito-cheng]

LGTM

clang/lib/Basic/Targets/RISCV.cpp

for (const std::string &Feature : FeaturesVec)
     if (!llvm::is_contained(ImpliedFeatures, Feature))
       ImpliedFeatures.push_back(Feature);
 
   return TargetInfo::initFeatureMap(Features, Diags, CPU, ImpliedFeatures);
 }
 
 std::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 (unsigned MinVLen = ISAInfo->getMinVLen();
-      MinVLen >= llvm::RISCV::RVVBitsPerBlock) {
-    unsigned MaxVLen = ISAInfo->getMaxVLen();
-    // RISCV::RVVBitsPerBlock is 64.
-    return std::make_pair(MinVLen / llvm::RISCV::RVVBitsPerBlock,
-                          MaxVLen / llvm::RISCV::RVVBitsPerBlock);
+  unsigned VScaleMin = ISAInfo->getMinVLen() / llvm::RISCV::RVVBitsPerBlock;
+
+  if (LangOpts.VScaleMin || LangOpts.VScaleMax) {
+    // Treat Zvl*b as a lower bound on vscale.
+    VScaleMin = std::max(VScaleMin, LangOpts.VScaleMin);
+    unsigned VScaleMax = LangOpts.VScaleMax;
+    if (VScaleMax != 0 && VScaleMax < VScaleMin)
+      VScaleMax = VScaleMin;
+    return std::pair<unsigned, unsigned>(VScaleMin ? VScaleMin : 1, VScaleMax);
+  }
+
+  if (VScaleMin > 0) {
+    unsigned VScaleMax = ISAInfo->getMaxVLen() / llvm::RISCV::RVVBitsPerBlock;
+    return std::make_pair(VScaleMin, VScaleMax);
   }
 
   return std::nullopt;
 }
 
 /// Return true if has this feature, need to sync with handleTargetFeatures.
 bool RISCVTargetInfo::hasFeature(StringRef Feature) const {
   bool Is64Bit = getTriple().getArch() == llvm::Triple::riscv64;

clang/test/CodeGen/riscv-vector-bits-vscale-range.c

-// 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 +zve64x -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 +zve64x -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 +zve64x -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-V
 // RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +v -target-feature +zvl512b -S -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-ZVL
 // RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +zve64x -S -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-ZVE64
 // RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +zve64f -target-feature +f -S -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-ZVE64
 // RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +zve64d -target-feature +f -target-feature +d -S -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-ZVE64
 // RUN: %clang_cc1 -triple riscv64-none-linux-gnu -target-feature +zve32x -S -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-ZVE32
 
 // CHECK-LABEL: @func() #0