[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 +1,400 @@
+// Check no warnings/errors
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fopenmp -std=c++20 -fopenmp-version=60 -fsyntax-only -verify %s
+// expected-no-diagnostics
+
+// Check AST and unparsing 
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fopenmp -std=c++20 -fopenmp-version=60 -ast-dump  %s | FileCheck %s --check-prefix=DUMP
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fopenmp -std=c++20 -fopenmp-version=60 -ast-print %s | FileCheck %s --check-prefix=PRINT
+
+// Check same results after serialization round-trip 
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fopenmp -std=c++20 -fopenmp-version=60 -emit-pch -o %t %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fopenmp -std=c++20 -fopenmp-version=60 -include-pch %t -ast-dump-all %s | FileCheck %s --check-prefix=DUMP
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -fopenmp -std=c++20 -fopenmp-version=60 -include-pch %t -ast-print    %s | FileCheck %s --check-prefix=PRINT
+
+#ifndef HEADER
+#define HEADER 
+
+// placeholder for loop body code
+extern "C" void body(...);
+
+// PRINT-LABEL: void foo1(
+// DUMP-LABEL: FunctionDecl {{.*}} foo1
+void foo1() {
+    // PRINT: #pragma omp fuse
+    // DUMP:  OMPFuseDirective
+    #pragma omp fuse 
+    // PRINT: {
+    // DUMP: CompoundStmt       
+    {
+        // PRINT: for (int i = 0; i < 10; i += 2)
+        // DUMP: ForStmt
+        for (int i = 0; i < 10; i += 2)
+            // PRINT: body(i)
+            // DUMP: CallExpr
+            body(i);
+        // PRINT: for (int j = 10; j > 0; --j)
+        // DUMP: ForStmt
+        for (int j = 10; j > 0; --j)
+            // PRINT: body(j)
+            // DUMP: CallExpr
+            body(j);
+        // PRINT: for (int k = 0; k <= 10; ++k)
+        // DUMP: ForStmt
+        for (int k = 0; k <= 10; ++k)
+            // PRINT: body(k)
+            // DUMP: CallExpr
+            body(k);
+
+    }
+
+}
+
+// PRINT-LABEL: void foo2(
+// DUMP-LABEL: FunctionDecl {{.*}} foo2
+void foo2() {
+    // PRINT: #pragma omp unroll partial(4)
+    // DUMP: OMPUnrollDirective
+    // DUMP-NEXT: OMPPartialClause
+    // DUMP-NEXT: ConstantExpr
+    // DUMP-NEXT: value: Int 4
+    // DUMP-NEXT: IntegerLiteral {{.*}} 4
+    #pragma omp unroll partial(4)
+    // PRINT: #pragma omp fuse
+    // DUMP-NEXT: OMPFuseDirective 
+    #pragma omp fuse 
+    // PRINT: {
+    // DUMP: CompoundStmt       
+    {
+        // PRINT: for (int i = 0; i < 10; i += 2)
+        // DUMP: ForStmt
+        for (int i = 0; i < 10; i += 2)
+            // PRINT: body(i)
+            // DUMP: CallExpr
+            body(i);
+        // PRINT: for (int j = 10; j > 0; --j)
+        // DUMP: ForStmt
+        for (int j = 10; j > 0; --j)
+            // PRINT: body(j)
+            // DUMP: CallExpr
+            body(j);  
+    }    
+    
+}
+
+//PRINT-LABEL: void foo3(
+//DUMP-LABEL: FunctionTemplateDecl {{.*}} foo3
+template<int Factor1, int Factor2> 
+void foo3() {
+    // PRINT:  #pragma omp fuse
+    // DUMP: OMPFuseDirective
+    #pragma omp fuse 
+    // PRINT: {
+    // DUMP: CompoundStmt       
+    {
+        // PRINT: #pragma omp unroll partial(Factor1)
+        // DUMP: OMPUnrollDirective
+        #pragma omp unroll partial(Factor1)
+        // PRINT: for (int i = 0; i < 12; i += 1)
+        // DUMP: ForStmt
+        for (int i = 0; i < 12; i += 1)
+            // PRINT: body(i)
+            // DUMP: CallExpr
+            body(i);
+        // PRINT: #pragma omp unroll partial(Factor2)
+        // DUMP: OMPUnrollDirective
+        #pragma omp unroll partial(Factor2)
+        // PRINT: for (int k = 0; k <= 10; ++k)
+        // DUMP: ForStmt
+        for (int k = 0; k <= 10; ++k)
+            // PRINT: body(k)
+            // DUMP: CallExpr
+            body(k);
+
+    }
+}
+
+// Also test instantiating the template.
+void tfoo3() {
+    foo3<4,2>();
+}
+
+//PRINT-LABEL: void foo4(
+//DUMP-LABEL: FunctionTemplateDecl {{.*}} foo4
+template<typename T, T Step> 
+void foo4(int start, int end) {
+    // PRINT:  #pragma omp fuse
+    // DUMP: OMPFuseDirective
+    #pragma omp fuse 
+    // PRINT: {
+    // DUMP: CompoundStmt       
+    {
+        // PRINT: for (T i = start; i < end; i += Step)
+        // DUMP: ForStmt
+        for (T i = start; i < end; i += Step)
+            // PRINT: body(i)
+            // DUMP: CallExpr
+            body(i);
+
+        // PRINT: for (T j = end; j > start; j -= Step)
+        // DUMP: ForStmt 
+        for (T j = end; j > start; j -= Step) {
+            // PRINT: body(j)
+            // DUMP: CallExpr
+            body(j);
+        }
+
+    }
+}
+
+// Also test instantiating the template.
+void tfoo4() {
+    foo4<int, 4>(0, 64);
+}
+
+
+
+// PRINT-LABEL: void foo5(
+// DUMP-LABEL: FunctionDecl {{.*}} foo5
+void foo5() {
+    double arr[128], arr2[128];
+    // PRINT: #pragma omp fuse
+    // DUMP:  OMPFuseDirective
+    #pragma omp fuse 
+    // PRINT: {
+    // DUMP: CompoundStmt       
+    {
+        // PRINT-NEXT: for (auto &&a : arr)
+        // DUMP-NEXT: CXXForRangeStmt
+        for (auto &&a: arr)
+            // PRINT: body(a)
+            // DUMP: CallExpr
+            body(a);
+        // PRINT: for (double v = 42; auto &&b : arr)
+        // DUMP: CXXForRangeStmt
+        for (double v = 42; auto &&b: arr)
+            // PRINT: body(b, v);
+            // DUMP: CallExpr
+            body(b, v);
+        // PRINT: for (auto &&c : arr2)
+        // DUMP: CXXForRangeStmt
+        for (auto &&c: arr2)
+            // PRINT: body(c)
+            // DUMP: CallExpr
+            body(c);
+
+    }
+
----------------
Meinersbur wrote:

```suggestion
    }
```
[nit] (other redundant empty lines too)

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