================
@@ -263,6 +264,72 @@ static void terminateBody(CIRGenBuilderTy &builder,
mlir::Region &r,
b->erase();
}
+mlir::LogicalResult CIRGenFunction::emitIfStmt(const IfStmt &s) {
+ mlir::LogicalResult res = mlir::success();
+ // The else branch of a consteval if statement is always the only branch
+ // that can be runtime evaluated.
+ const Stmt *ConstevalExecuted;
+ if (s.isConsteval()) {
+ ConstevalExecuted = s.isNegatedConsteval() ? s.getThen() : s.getElse();
+ if (!ConstevalExecuted) {
+ // No runtime code execution required
+ return res;
+ }
+ }
+
+ // C99 6.8.4.1: The first substatement is executed if the expression
+ // compares unequal to 0. The condition must be a scalar type.
+ auto ifStmtBuilder = [&]() -> mlir::LogicalResult {
+ if (s.isConsteval())
+ return emitStmt(ConstevalExecuted, /*useCurrentScope=*/true);
+
+ if (s.getInit())
+ if (emitStmt(s.getInit(), /*useCurrentScope=*/true).failed())
+ return mlir::failure();
+
+ if (s.getConditionVariable())
+ emitDecl(*s.getConditionVariable());
+
+ // During LLVM codegen, if the condition constant folds and can be elided,
+ // it tries to avoid emitting the condition and the dead arm of the
if/else.
+ // TODO(cir): we skip this in CIRGen, but should implement this as part of
+ // SSCP or a specific CIR pass.
+ bool CondConstant;
+ if (ConstantFoldsToSimpleInteger(s.getCond(), CondConstant,
----------------
andykaylor wrote:
> Doing it in MLIR is probably nicer, but if we can "easily" (not too compile
> time intensive) do it during CIRGen, shouldn't we?
I guess this is a philosophical question, but I'm of the opinion that the front
end should strictly be producing IR that represents the semantics of the source
code and has no business doing any sort of optimization. It took me a while to
come to this conclusion when I was working on the optimizer, because it was
jarring how inefficient the IR looked coming out of the front end (things like
storing a variable to an alloca slot and then immediately reloading it, but I
eventually came to realize that the front end was doing that because those were
the unvarnished semantics of the source code. Taking that to the extreme, if
the source code says "if (true)..." what business does the front end have
removing that? Optimizations should be left to the optimizer.
https://github.com/llvm/llvm-project/pull/134333
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