[clang] [Clang] Fix incorrect handling of #pragma {GCC} unroll N in dependent context (PR #90240)

[via cfe-commits]

https://github.com/yronglin updated https://github.com/llvm/llvm-project/pull/90240

>From 131783211a23d007b5b6f1d5691306df4dec716b Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Sat, 27 Apr 2024 01:38:34 +0800
Subject: [PATCH 1/2] [Clang] Fix incorrect handling of #pragma {GCC} unroll N
 in dependent context

Signed-off-by: yronglin <yronglin777 at gmail.com>
---
 clang/lib/Sema/SemaStmtAttr.cpp     | 23 ++++++++++--------
 clang/test/Parser/pragma-unroll.cpp | 37 +++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/clang/lib/Sema/SemaStmtAttr.cpp b/clang/lib/Sema/SemaStmtAttr.cpp
index 9d44c22c8ddcc3..4dfdfd7aec425f 100644
--- a/clang/lib/Sema/SemaStmtAttr.cpp
+++ b/clang/lib/Sema/SemaStmtAttr.cpp
@@ -109,16 +109,19 @@ static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const ParsedAttr &A,
     SetHints(LoopHintAttr::Unroll, LoopHintAttr::Disable);
   } else if (PragmaName == "unroll") {
     // #pragma unroll N
-    if (ValueExpr && !ValueExpr->isValueDependent()) {
-      llvm::APSInt ValueAPS;
-      ExprResult R = S.VerifyIntegerConstantExpression(ValueExpr, &ValueAPS);
-      assert(!R.isInvalid() && "unroll count value must be a valid value, it's "
-                               "should be checked in Sema::CheckLoopHintExpr");
-      (void)R;
-      // The values of 0 and 1 block any unrolling of the loop.
-      if (ValueAPS.isZero() || ValueAPS.isOne())
-        SetHints(LoopHintAttr::UnrollCount, LoopHintAttr::Disable);
-      else
+    if (ValueExpr) {
+      if (!ValueExpr->isValueDependent()) {
+        llvm::APSInt ValueAPS;
+        ExprResult R = S.VerifyIntegerConstantExpression(ValueExpr, &ValueAPS);
+        assert(!R.isInvalid() && "unroll count value must be a valid value, it's "
+                                "should be checked in Sema::CheckLoopHintExpr");
+        (void)R;
+        // The values of 0 and 1 block any unrolling of the loop.
+        if (ValueAPS.isZero() || ValueAPS.isOne())
+          SetHints(LoopHintAttr::UnrollCount, LoopHintAttr::Disable);
+        else
+          SetHints(LoopHintAttr::UnrollCount, LoopHintAttr::Numeric);
+      } else
         SetHints(LoopHintAttr::UnrollCount, LoopHintAttr::Numeric);
     } else
       SetHints(LoopHintAttr::Unroll, LoopHintAttr::Enable);
diff --git a/clang/test/Parser/pragma-unroll.cpp b/clang/test/Parser/pragma-unroll.cpp
index f41bd7a18d5a41..e84f6ea9ad1035 100644
--- a/clang/test/Parser/pragma-unroll.cpp
+++ b/clang/test/Parser/pragma-unroll.cpp
@@ -124,3 +124,40 @@ void test(int *List, int Length) {
 
 #pragma unroll
 /* expected-error {{expected statement}} */ }
+
+using size_t = unsigned long long;
+
+template <bool Flag>
+int FailToBuild(int n) {
+  constexpr int N = 100;
+  auto init = [=]() { return Flag ? n : 0UL; };
+  auto cond = [=](size_t ix) { return Flag ? ix != 0 : ix < 10; };
+  auto iter = [=](size_t ix) {
+    return Flag ? ix & ~(1ULL << __builtin_clzll(ix)) : ix + 1;
+  };
+#pragma unroll Flag ? 1 : N
+  for (size_t ix = init(); cond(ix); ix = iter(ix)) {
+    n *= n;
+  }
+#pragma unroll Flag ? 0 : N
+  for (size_t ix = init(); cond(ix); ix = iter(ix)) {
+    n *= n;
+  }
+#pragma GCC unroll Flag ? 1 : N
+  for (size_t ix = init(); cond(ix); ix = iter(ix)) {
+    n *= n;
+  }
+#pragma GCC unroll Flag ? 0 : N
+  for (size_t ix = init(); cond(ix); ix = iter(ix)) {
+    n *= n;
+  }
+  return n;
+}
+
+int foo(int n) {
+    return FailToBuild<true>(n);
+}
+
+int bar(int n) {
+    return FailToBuild<false>(n);
+}

>From 3e5ef859c3d55830199a366edf48a8f536dc1208 Mon Sep 17 00:00:00 2001
From: yronglin <yronglin777 at gmail.com>
Date: Sat, 27 Apr 2024 01:52:41 +0800
Subject: [PATCH 2/2] Format

Signed-off-by: yronglin <yronglin777 at gmail.com>
---
 clang/lib/Sema/SemaStmtAttr.cpp | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Sema/SemaStmtAttr.cpp b/clang/lib/Sema/SemaStmtAttr.cpp
index 4dfdfd7aec425f..d3e76f282974e9 100644
--- a/clang/lib/Sema/SemaStmtAttr.cpp
+++ b/clang/lib/Sema/SemaStmtAttr.cpp
@@ -113,8 +113,9 @@ static Attr *handleLoopHintAttr(Sema &S, Stmt *St, const ParsedAttr &A,
       if (!ValueExpr->isValueDependent()) {
         llvm::APSInt ValueAPS;
         ExprResult R = S.VerifyIntegerConstantExpression(ValueExpr, &ValueAPS);
-        assert(!R.isInvalid() && "unroll count value must be a valid value, it's "
-                                "should be checked in Sema::CheckLoopHintExpr");
+        assert(!R.isInvalid() &&
+               "unroll count value must be a valid value, it's "
+               "should be checked in Sema::CheckLoopHintExpr");
         (void)R;
         // The values of 0 and 1 block any unrolling of the loop.
         if (ValueAPS.isZero() || ValueAPS.isOne())