[clang] [flang] [llvm] [openmp] [Clang][OpenMP][LoopTransformations] Add support for "#pragma omp fuse" loop transformation directive and "looprange" clause (PR #139293)

[Michael Kruse via llvm-commits]

================
@@ -0,0 +1,211 @@
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -std=c++20 -fopenmp -fopenmp-version=60 -fsyntax-only -Wuninitialized -verify %s
+
+void func() {
+
+    // expected-error at +2 {{statement after '#pragma omp fuse' must be a loop sequence containing canonical loops or loop-generating constructs}}
+    #pragma omp fuse 
+    ;
+
+    // expected-error at +2 {{statement after '#pragma omp fuse' must be a for loop}}
+    #pragma omp fuse 
+    {int bar = 0;}
+
+    // expected-error at +4 {{statement after '#pragma omp fuse' must be a for loop}}
+    #pragma omp fuse 
+    {
+        for(int i = 0; i < 10; ++i);
+        int x = 2;
+    }
+
+    // expected-error at +2 {{statement after '#pragma omp fuse' must be a loop sequence containing canonical loops or loop-generating constructs}}
+    #pragma omp fuse 
+    #pragma omp for 
+    for (int i = 0; i < 7; ++i)
+        ;
+
+    {
+        // expected-error at +2 {{expected statement}}
+        #pragma omp fuse
+    }
+
+    // expected-warning at +1 {{extra tokens at the end of '#pragma omp fuse' are ignored}}
+    #pragma omp fuse foo
+    {
+        for (int i = 0; i < 7; ++i)
+            ;
+        for(int j = 0; j < 100; ++j);
+
+    }
+
+
+    // expected-error at +1 {{unexpected OpenMP clause 'final' in directive '#pragma omp fuse'}}
+    #pragma omp fuse final(0) 
+    {
+        for (int i = 0; i < 7; ++i)
+            ;
+        for(int j = 0; j < 100; ++j);
+
+    }
+
+    //expected-error at +4 {{loop after '#pragma omp fuse' is not in canonical form}}
+    //expected-error at +3 {{increment clause of OpenMP for loop must perform simple addition or subtraction on loop variable 'i'}}
+    #pragma omp fuse 
+    {
+        for(int i = 0; i < 10; i*=2) {
+            ;
+        }
+        for(int j = 0; j < 100; ++j);
+    }
+
+    //expected-error at +2 {{loop sequence after '#pragma omp fuse' must contain at least 1 canonical loop or loop-generating construct}}
+    #pragma omp fuse 
+    {}
+
+    //expected-error at +3 {{statement after '#pragma omp fuse' must be a for loop}}
+    #pragma omp fuse 
+    {
+        #pragma omp unroll full 
+        for(int i = 0; i < 10; ++i);
+        
+        for(int j = 0; j < 10; ++j);
+    }
+
+    //expected-warning at +2 {{loop range in '#pragma omp fuse' contains only a single loop, resulting in redundant fusion}}
+    #pragma omp fuse
+    {
+        for(int i = 0; i < 10; ++i);
+    }
+
+    //expected-warning at +1 {{loop range in '#pragma omp fuse' contains only a single loop, resulting in redundant fusion}}
+    #pragma omp fuse looprange(1, 1)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+    }
+
+    //expected-error at +1 {{argument to 'looprange' clause must be a strictly positive integer value}}
+    #pragma omp fuse looprange(1, -1)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+    }
+
+    //expected-error at +1 {{argument to 'looprange' clause must be a strictly positive integer value}}
+    #pragma omp fuse looprange(1, 0)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+    }
+
+    const int x = 1;
+    constexpr int y = 4;
+    //expected-error at +1 {{loop range in '#pragma omp fuse' exceeds the number of available loops: range end '4' is greater than the total number of loops '3'}}
+    #pragma omp fuse looprange(x,y)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+        for(int k = 0; k < 50; ++k);
+    }
+
+    //expected-error at +1 {{loop range in '#pragma omp fuse' exceeds the number of available loops: range end '420' is greater than the total number of loops '3'}}
+    #pragma omp fuse looprange(1,420)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+        for(int k = 0; k < 50; ++k);
+    }
+
+    //expected-error at +1 {{loop range in '#pragma omp fuse' exceeds the number of available loops: range end '6' is greater than the total number of loops '5'}}
+    #pragma omp fuse looprange(1,6)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+        for(int k = 0; k < 50; ++k);
+        // This fusion results in  2 loops
+        #pragma omp fuse looprange(1,2)
+        {
+            for(int i = 0; i < 10; ++i);
+            for(int j = 0; j < 100; ++j);
+            for(int k = 0; k < 50; ++k);
+        }
+    }
+
+    //expected-error at +1 {{loop range in '#pragma omp fuse' exceeds the number of available loops: range end '4' is greater than the total number of loops '3'}}
+    #pragma omp fuse looprange(2,3)
+    {
+        #pragma omp unroll partial(2)
+        for(int i = 0; i < 10; ++i);
+        
+        #pragma omp reverse
+        for(int j = 0; j < 10; ++j);
+
+        #pragma omp fuse 
+        {
+            {
+                #pragma omp reverse
+                for(int j = 0; j < 10; ++j);
+            }            
+            for(int k = 0; k < 50; ++k);
+        }
+    }
+}
+
+// In a template context, but expression itself not instantiation-dependent
+template <typename T>
+static void templated_func() {
+
+    //expected-warning at +1 {{loop range in '#pragma omp fuse' contains only a single loop, resulting in redundant fusion}}
+    #pragma omp fuse looprange(2,1)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+        for(int k = 0; k < 50; ++k);
+    }
+
+    //expected-error at +1 {{loop range in '#pragma omp fuse' exceeds the number of available loops: range end '5' is greater than the total number of loops '3'}}
+    #pragma omp fuse looprange(3,3)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+        for(int k = 0; k < 50; ++k);
+    }
+
+}
+
+template <int V> 
+static void templated_func_value_dependent() {
+
+    //expected-warning at +1 {{loop range in '#pragma omp fuse' contains only a single loop, resulting in redundant fusion}}
+    #pragma omp fuse looprange(V,1)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+        for(int k = 0; k < 50; ++k);
+    }
+}
+
+template <typename T> 
+static void templated_func_type_dependent() {
+    constexpr T s = 1;
+
+    //expected-error at +1 {{argument to 'looprange' clause must be a strictly positive integer value}}
+    #pragma omp fuse looprange(s,s-1)
+    {
+        for(int i = 0; i < 10; ++i);
+        for(int j = 0; j < 100; ++j);
+        for(int k = 0; k < 50; ++k);
+    }
+}
+
+
+void template_inst() {
+    // expected-note at +1 {{in instantiation of function template specialization 'templated_func<int>' requested here}}
+    templated_func<int>();
+    // expected-note at +1 {{in instantiation of function template specialization 'templated_func_value_dependent<1>' requested here}}
+    templated_func_value_dependent<1>();
+    // expected-note at +1 {{in instantiation of function template specialization 'templated_func_type_dependent<int>' requested here}}
+    templated_func_type_dependent<int>();
+
----------------
Meinersbur wrote:

```suggestion
```
[nit]

https://github.com/llvm/llvm-project/pull/139293