[clang] [RISCV] Enable target attribute when invoked through clang driver (PR #74889)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Philip Reames (preames)

<details>
<summary>Changes</summary>

d80e46d added support for the target function attribute.  However, it turns out that commit has a nasty bug/oversight.  As the tests in that revision show, everything works if clang -cc1 is directly invoked.  I was suprised to learn this morning that compiling with clang (i.e. the typical user workflow) did not work.

The bug is that if a set of explicit negative extensions is passed to cc1 at the command line (as the clang driver always does), we were copying these negative extensions to the end of the rewritten extension list.  When this was later parsed, this had the effect of turning back off any extension that the target attribute had enabled.

This patch updates the logic to only propagate the features from the input which don't appear in the rewritten form in either positive or negative form.

Note that this code structure is still highly suspect.  In particular I'm fairly sure that mixing extension versions with this code will result in odd results.  However, I figure its better to have something which mostly works than something which doesn't work at all.

---
Full diff: https://github.com/llvm/llvm-project/pull/74889.diff


2 Files Affected:

- (modified) clang/lib/Basic/Targets/RISCV.cpp (+11-4) 
- (modified) clang/test/CodeGen/RISCV/riscv-func-attr-target.c (+11-10) 


``````````diff
diff --git a/clang/lib/Basic/Targets/RISCV.cpp b/clang/lib/Basic/Targets/RISCV.cpp
index 13f934e994721..184176c05da23 100644
--- a/clang/lib/Basic/Targets/RISCV.cpp
+++ b/clang/lib/Basic/Targets/RISCV.cpp
@@ -304,11 +304,18 @@ bool RISCVTargetInfo::initFeatureMap(
 
   // RISCVISAInfo makes implications for ISA features
   std::vector<std::string> ImpliedFeatures = (*ParseResult)->toFeatureVector();
-  // Add non-ISA features like `relax` and `save-restore` back
-  for (const std::string &Feature : NewFeaturesVec)
-    if (!llvm::is_contained(ImpliedFeatures, Feature))
-      ImpliedFeatures.push_back(Feature);
 
+  // parseFeatures normalizes the feature set by dropping any explicit
+  // negatives, and non-extension features.  We need to preserve the later
+  // for correctness and want to preserve the former for consistency.
+  for (auto &Feature : NewFeaturesVec) {
+     StringRef ExtName = Feature;
+     assert(ExtName.size() > 1 && (ExtName[0] == '+' || ExtName[0] == '-'));
+     ExtName = ExtName.drop_front(1); // Drop '+' or '-'
+     if (!llvm::is_contained(ImpliedFeatures, ("+" + ExtName).str()) &&
+         !llvm::is_contained(ImpliedFeatures, ("-" + ExtName).str()))
+       ImpliedFeatures.push_back(Feature);
+  }
   return TargetInfo::initFeatureMap(Features, Diags, CPU, ImpliedFeatures);
 }
 
diff --git a/clang/test/CodeGen/RISCV/riscv-func-attr-target.c b/clang/test/CodeGen/RISCV/riscv-func-attr-target.c
index 74bc5f2ac7049..506acaba68741 100644
--- a/clang/test/CodeGen/RISCV/riscv-func-attr-target.c
+++ b/clang/test/CodeGen/RISCV/riscv-func-attr-target.c
@@ -1,6 +1,7 @@
 // REQUIRES: riscv-registered-target
 // RUN: %clang_cc1 -triple riscv64 -target-feature +zifencei -target-feature +m \
-// RUN:  -target-feature +a -target-feature +save-restore \
+// RUN:  -target-feature +a -target-feature +save-restore -target-feature -zbb \
+// RUN:  -target-feature -relax -target-feature -zfa \
 // RUN:  -emit-llvm %s -o - | FileCheck %s
 
 // CHECK-LABEL: define dso_local void @testDefault
@@ -35,12 +36,12 @@ testAttrFullArchAndAttrCpu() {}
 __attribute__((target("cpu=sifive-u54"))) void testAttrCpuOnly() {}
 
 //.
-// CHECK: attributes #0 = { {{.*}}"target-features"="+64bit,+a,+m,+save-restore,+zifencei" }
-// CHECK: attributes #1 = { {{.*}}"target-cpu"="rocket-rv64" "target-features"="+64bit,+a,+d,+f,+m,+save-restore,+v,+zicsr,+zifencei,+zve32f,+zve32x,+zve64d,+zve64f,+zve64x,+zvl128b,+zvl32b,+zvl64b" "tune-cpu"="generic-rv64" }
-// CHECK: attributes #2 = { {{.*}}"target-features"="+64bit,+a,+m,+save-restore,+zbb,+zifencei" }
-// CHECK: attributes #3 = { {{.*}}"target-features"="+64bit,+a,+d,+experimental-zicond,+f,+m,+save-restore,+v,+zbb,+zicsr,+zifencei,+zve32f,+zve32x,+zve64d,+zve64f,+zve64x,+zvl128b,+zvl32b,+zvl64b" }
-// CHECK: attributes #4 = { {{.*}}"target-features"="+64bit,+a,+c,+d,+f,+m,+save-restore,+zbb,+zicsr,+zifencei" }
-// CHECK: attributes #5 = { {{.*}}"target-features"="+64bit,+m,+save-restore" }
-// CHECK: attributes #6 = { {{.*}}"target-cpu"="sifive-u54" "target-features"="+64bit,+a,+m,+save-restore,+zbb,+zifencei" }
-// CHECK: attributes #7 = { {{.*}}"target-cpu"="sifive-u54" "target-features"="+64bit,+m,+save-restore" }
-// CHECK: attributes #8 = { {{.*}}"target-cpu"="sifive-u54" "target-features"="+64bit,+a,+c,+d,+f,+m,+save-restore,+zicsr,+zifencei" }
+// CHECK: attributes #0 = { {{.*}}"target-features"="+64bit,+a,+m,+save-restore,+zifencei,-relax,-zbb,-zfa" }
+// CHECK: attributes #1 = { {{.*}}"target-cpu"="rocket-rv64" "target-features"="+64bit,+a,+d,+f,+m,+save-restore,+v,+zicsr,+zifencei,+zve32f,+zve32x,+zve64d,+zve64f,+zve64x,+zvl128b,+zvl32b,+zvl64b,-relax,-zbb,-zfa" "tune-cpu"="generic-rv64" }
+// CHECK: attributes #2 = { {{.*}}"target-features"="+64bit,+a,+m,+save-restore,+zbb,+zifencei,-relax,-zfa" }
+// CHECK: attributes #3 = { {{.*}}"target-features"="+64bit,+a,+d,+experimental-zicond,+f,+m,+save-restore,+v,+zbb,+zicsr,+zifencei,+zve32f,+zve32x,+zve64d,+zve64f,+zve64x,+zvl128b,+zvl32b,+zvl64b,-relax,-zfa" }
+// CHECK: attributes #4 = { {{.*}}"target-features"="+64bit,+a,+c,+d,+f,+m,+save-restore,+zbb,+zicsr,+zifencei,-relax,-zfa" }
+// CHECK: attributes #5 = { {{.*}}"target-features"="+64bit,+m,+save-restore,-relax,-zbb,-zfa" }
+// CHECK: attributes #6 = { {{.*}}"target-cpu"="sifive-u54" "target-features"="+64bit,+a,+m,+save-restore,+zbb,+zifencei,-relax,-zfa" }
+// CHECK: attributes #7 = { {{.*}}"target-cpu"="sifive-u54" "target-features"="+64bit,+m,+save-restore,-relax,-zbb,-zfa" }
+// CHECK: attributes #8 = { {{.*}}"target-cpu"="sifive-u54" "target-features"="+64bit,+a,+c,+d,+f,+m,+save-restore,+zicsr,+zifencei,-relax,-zbb,-zfa" }

``````````

</details>


https://github.com/llvm/llvm-project/pull/74889