[clang] [llvm] [HLSL] Add support to branch/flatten attributes to switch (PR #131739)

[Sarah Spall via llvm-commits]

================
@@ -91,6 +91,137 @@ if.end:                                           ; preds = %if.else, %if.then
   %3 = load i32, ptr %resp, align 4
   ret i32 %3
 }
+
+; CHECK: define i32 @flatten_switch(i32 %X)
+; CHECK-NOT: hlsl.controlflow.hint
+; CHECK:      switch i32 %0, label %sw.epilog [
+; CHECK-NEXT:   i32 0, label %sw.bb
+; CHECK-NEXT:   i32 1, label %sw.bb1
+; CHECK-NEXT:   i32 2, label %sw.bb2
+; CHECK-NEXT: ], !dx.controlflow.hints [[HINT_FLATTEN]]
+define i32 @flatten_switch(i32 %X) #0 {
+entry:
+  %X.addr = alloca i32, align 4
+  %resp = alloca i32, align 4
+  store i32 %X, ptr %X.addr, align 4
+  %0 = load i32, ptr %X.addr, align 4
+  switch i32 %0, label %sw.epilog [
+    i32 0, label %sw.bb
+    i32 1, label %sw.bb1
+    i32 2, label %sw.bb2
+  ], !hlsl.controlflow.hint !1
+
+sw.bb:                                            ; preds = %entry
+  %1 = load i32, ptr %X.addr, align 4
+  %sub = sub nsw i32 0, %1
+  store i32 %sub, ptr %resp, align 4
+  br label %sw.epilog
+
+sw.bb1:                                           ; preds = %entry
+  %2 = load i32, ptr %X.addr, align 4
+  %3 = load i32, ptr %X.addr, align 4
+  %add = add nsw i32 %2, %3
+  store i32 %add, ptr %resp, align 4
+  br label %sw.epilog
+
+sw.bb2:                                           ; preds = %entry
+  %4 = load i32, ptr %X.addr, align 4
+  %5 = load i32, ptr %X.addr, align 4
+  %mul = mul nsw i32 %4, %5
+  store i32 %mul, ptr %resp, align 4
+  br label %sw.epilog
+
+sw.epilog:                                        ; preds = %entry, %sw.bb2, %sw.bb1, %sw.bb
+  %6 = load i32, ptr %resp, align 4
+  ret i32 %6
+}
+
+
+; CHECK: define i32 @branch_switch(i32 %X)
+; CHECK-NOT: hlsl.controlflow.hint
+; CHECK:      switch i32 %0, label %sw.epilog [
+; CHECK-NEXT:   i32 0, label %sw.bb
+; CHECK-NEXT:   i32 1, label %sw.bb1
+; CHECK-NEXT:   i32 2, label %sw.bb2
+; CHECK-NEXT: ], !dx.controlflow.hints [[HINT_BRANCH]]
----------------
spall wrote:

is HINT_BRANCH supposed to be a 0?

https://github.com/llvm/llvm-project/pull/131739