[flang-commits] [flang] [flang] Simplify the comparison of characters (PR #154593)

[Leandro Lupori via flang-commits]

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@@ -0,0 +1,294 @@
+#include "flang/Optimizer/Builder/FIRBuilder.h"
+#include "flang/Optimizer/HLFIR/HLFIROps.h"
+#include "flang/Optimizer/HLFIR/Passes.h"
+#include "flang/Runtime/entry-names.h"
+#include "llvm/Support/DebugLog.h"
+
+namespace hlfir {
+#define GEN_PASS_DEF_EXPRESSIONSIMPLIFICATION
+#include "flang/Optimizer/HLFIR/Passes.h.inc"
+} // namespace hlfir
+
+#define DEBUG_TYPE "expression-simplification"
+
+#define INDENT(n) std::string((n) * 2, ' ')
+
+static void removeOperands(mlir::Operation *op, int nestLevel);
+
+static void removeOp(mlir::Operation *op, int parentUses, int nestLevel) {
+  int opUses = std::distance(op->getUses().begin(), op->getUses().end());
+
+  if (opUses <= parentUses) {
+    LDBG() << INDENT(nestLevel) << "remove: " << *op;
+    removeOperands(op, nestLevel);
+    op->dropAllReferences();
+    op->dropAllUses();
+    op->erase();
+  }
+}
+
+static void removeOp(mlir::Operation *op) {
+  removeOp(op, /*parentUses=*/0, /*nestLevel=*/0);
+  LDBG();
+}
+
+static void removeOperands(mlir::Operation *op, int nestLevel) {
+  for (mlir::Value operand : op->getOperands()) {
+    if (!operand)
+      // Already removed.
+      continue;
+    if (mlir::Operation *operandOp = operand.getDefiningOp()) {
+      int uses = 0;
+      for (mlir::Operation *user : operandOp->getUsers())
+        if (user == op)
+          ++uses;
+      removeOp(operandOp, uses, nestLevel + 1);
+    }
+  }
+}
+
+template <typename UserOp>
+static UserOp getFirstUser(mlir::Operation *op) {
+  auto it = op->user_begin(), end = op->user_end(), prev = it;
+  for (; it != end; prev = it++)
+    ;
+  if (prev != end)
+    if (auto userOp = mlir::dyn_cast<UserOp>(*prev))
+      return userOp;
+  return {};
+}
+
+template <typename UserOp>
+static UserOp getLastUser(mlir::Operation *op) {
+  if (!op->getUsers().empty())
+    if (auto userOp = mlir::dyn_cast<UserOp>(*op->user_begin()))
+      return userOp;
+  return {};
+}
+
+template <typename UserOp>
+static UserOp getPreviousUser(mlir::Operation *op, mlir::Operation *curUser) {
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luporl wrote:

What I have observed is that the user at `begin` is on the highest line in the emitted HLFIR, while `--end` is on the lowest one. That's why it made more sense to me to name these functions in this way, instead of considering the first user to be that returned by `begin`.

Do you think it would be OK to just add a comment explaining this?

https://github.com/llvm/llvm-project/pull/154593