[flang] Use llvm.zext when converting from i1 -> iXX

CodeGen used llvm.sext when converting fir.convert %0 : (i1) -> iXX
where iXX is any integer. This leads to wrong values when the initial
i1 is equal to 1.

Reviewed By: PeteSteinfeld

Differential Revision: https://reviews.llvm.org/D145984

Author: clementval

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -937,6 +937,10 @@ struct ConvertOpConversion : public FIROpConversion<fir::ConvertOp> {
           rewriter.replaceOpWithNewOp<mlir::LLVM::TruncOp>(convert, toTy, op0);
           return mlir::success();
         }
+        if (fromFirTy == i1Type) {
+          rewriter.replaceOpWithNewOp<mlir::LLVM::ZExtOp>(convert, toTy, op0);
+          return mlir::success();
+        }
         rewriter.replaceOpWithNewOp<mlir::LLVM::SExtOp>(convert, toTy, op0);
         return mlir::success();
       }

flang/test/Fir/convert-to-llvm.fir

@@ -739,6 +739,16 @@ func.func @convert_from_int(%arg0 : i32) {
 // CHECK:         %{{.*}} = llvm.sext %[[ARG0]] : i32 to i64
 // CHECK:         %{{.*}} = llvm.inttoptr %{{.*}} : i64 to !llvm.ptr<i64>
 
+
+func.func @convert_from_i1(%arg0 : i1) {
+  %0 = fir.convert %arg0 : (i1) -> i32
+  return
+}
+
+// CHECK-LABEL: convert_from_i1(
+// CHECK-SAME: %[[ARG0:.*]]: i1
+// CHECK:        %{{.*}} = llvm.zext %[[ARG0]] : i1 to i32 
+
 // -----
 
 // Test `fir.convert` operation conversion from !fir.ref<> type.